Louvered magnetically stabilized fluid cross-flow contactor and processes for using the same

ABSTRACT

Apparatus for effecting fluid-solids contacting wherein a bed of stationary or downward moving ferromagnetic particles are contacted within a contacting chamber with a fluid which passes through the bed in a cross-flow manner, said bed being structured or stabilized, by a magnetic field, the improvement which comprises providing louver means attached below at least one of the openings of the contacting chamber, said louver means which extend upward and outward from the openings in the direction of the incoming gaseous fluid and the balance of the louver extending outward and downward toward the incoming gaseous fluid stream. Also disclosed are processes for using the improved louvered magnetically stabilized crossflow contactor including processes for removing particulates from gaseous streams, flue gas desulfurization processes and the like.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a fluid cross-flow fluid-solidcontactor of the panel or radial reactor type wherein ferromagnetic bedsolids are structured or stabilized by the action of a magnetic field,and is particularly concerned with means for contacting fluids and solidparticles in one or more such cross-flow beds having an imposed magneticfield. The invention also relates to a method for removing particulatesfrom a gas containing the same and flue gas desulfurization processesutilizing a cross-flow or panel bed contactor stabilized by the actionof a magnetic field.

2. Description of the Prior Art

There is considerable interest in the field of fluid-solids contacting,particularly gaseous fluids. Such processes have found uses in coalgasification, catalytic reactions, gas absorption, gas adsorption, andfiltering particulate material from gases and flue gas desulfurizationprocesses. Many such processes are carried out in fluidized beds, i.e.,beds containing a mass of solid fluidizable particles in which theindividual particles are effectively buoyed by fluid drag forces wherebythe mass or fluidized bed possesses the characteristics of a liquid.These fluidized beds are conventionally produced by effecting a flow ofa fluid such as a gas through a porous or perforated plate or membraneunderlying the particle mass, at a sufficient rate to support theparticles against the force of gravity. Conditions at the minimum fluidflow required to produce the fluid-like, or fluidized conditions, i.e.,the incipient fluidization point are dependent or many parametersincluding particle size, particle density, etc. The increase in thefluid flow beyond the incipient fluidization point causes an expansionof the fluidized bed to accommodate the increased fluid flow until thefluid velocity exceeds the free falling velocity of the particles whichare then carried out of the apparatus, a condition known as entrainment.

Recently, U.S. Pat. No. 4,115,927, described a process for stabilizingsuch fluidized beds against bubble formation by use of an axiallyapplied magnetic field. The magnetically stabilized fluidized beds(MSFB) disclosed in the U.S. Pat. No. 4,115,927 are useful in thecarrying out the above-mentioned processes and particularly for removingsolid particulates entrained in gaseous fluids. One problem connectedwith using the MSFB of the type disclosed in the U.S. Pat. No. 4,115,927for particulate capture processes or other processes involvingparticulate containing gas streams, however, relates to plugging of thegrid or perforated plate underlying the particle mass, thus causingsubstantial pressure drops to develop during operations as well ascausing lost operating time while the grids are periodically cleaned.

A number of patents describe processes for the separation ofparticulates entrained in gaseous fluids by magnetic means. Suchprocesses, quite often require the particulates themselves to bemagnetic. One such process is described in U.S. Pat. No. 4,116,829. Inthis patent the gas containing the magnetic particulates entrained inthe gas is passed through a chamber containing ferromagnetic filamentswhich are magnetized by an external magnetic field. The magneticparticulates adhere to the filaments. The particulates then aresubsequently removed from the filaments.

Recently, J. R. Melcher at the Massachusetts Institute of Technologydisclosed electrofluidized beds (EFB) for the collection of particulatesentrained in a gaseous fluid. In such an EFB process, electrostaticfields are used to impress differential electric charges on theparticulates to be captured so as to effect an attraction between suchparticulates and bed particles. Such processes are disclosed in U.S.Pat. Nos. 4,038,049 and 4,038,052 and the publications: Zahedi andMelcher, J. Air Pollut. Contr., (1974). While Melcher et al. refer tocross-flow and colinear EFB's by the term cross-flow EFB's, theyactually describe contactors wherein the gas flow levitates thefluidizable particles as in the typical axial flow contactor. Typically,a cross-flow gas contactor is understood to be a contactor wherein thegas flows perpendicular to the external force field, i.e., gravity. TheEFB's described by Melcher et al. have been shown to be usefulcollecting particulates, especially submicron particulates. However, theEFB's having a vertical gas flow are unable to process gas streams atvelocities greater than 1 ft./sec. without encountering substantialpressure drops and/or entrainment of solids, e.g., using sand particles.

Cross-flow and panel bed fluid-solid contactors (i.e., where the fluid(gas) flow is perpendicular to gravity) are well-recognized means forcontacting solids and fluids (particularly gases), the first industrialuse being known as the Deacon process developed nearly 100 years ago.Perry's Chemical Engineers' Handbook, 5th Edition discloses details ofseveral fluid cross-flow contactors of the type described by Dorfan,Squires and Zenz. Such processes eliminate the need for a porous gridsuch as is required in fluidized beds of Rosensweig and Melcher et al.As reported by Squires and Pfeffer (J. of the Air Pollution ControlAssociation, Vol. 20, No. 8, pp. 534-538 (1970)) a considerable numberof patents have been directed to cross-flow or panel bed devices.Squires et al. reported that many of these patents are directed to meansfor regulating the flow of the gravitating solid or means forwithdrawing the solids. A number of patents have been granted on the useof panel beds as filters to remove particulates from gaseous streams. Inthese patents the panel beds are described as having each gas-entrysurface free of loose surface particles of the filter solid. The surfaceis generally inclined at the solid particles' angle of repose, and itrests upon a louver. The solid particles used in these processes aregenerally rather large. U.S. Pat. No. 3,296,775 to Squires disclosesthat filter cake and a controlled amount of filter solid can be removedfrom each gas-entry surface by applying a surge backflow of gas from theclean side of the panel. Various improvements have been described inU.S. Pat. Nos. 3,410,055; 4,006,533; 4,004,896; 3,982,326; 4,004,350;3,926,587; 3,926,593; 3,957,953; 3,981,355; 3,987,148; and 4,000,066.

U.S. Pat. Nos. 4,102,982 to Weir, Jr.; 4,017,278 and 4,126,435 to Reesealso disclose processes for removing finely divided solids from gaseousstreams by use of gas cross-flow contactors. The Reese patent disclosesthe use of louvered surfaces formed by perforating the walls to formlouver vanes inclined to the vertical at angles ranging from 15° to 80°.

U.S. Pat. No. 3,966,879 to Groenendaal et al. discloses a process forthe removal of particulate matter and sulfur oxides from waste gaseswhich comprise cross-current contacting of the waste gas stream with amoving bed of supported, copper-containing acceptor.

The panel-bed or cross-flow contactors described by Squires, Dorfan,Zenz, Groenendaal and others are limited by the amount of gas throughputthan can be tolerated before solids break-through using small particles.Therefore, the degree in which the particles can come into contact witha gas is limited.

In some industrial processes, particularly flue gas desulfurizationprocesses, relatively high superficial gas velocities, i.e., the orderof 2-8 ft./sec. (60-245 cm./sec.) and higher with particles having amean diameter size about 300-1000 microns are desired. The highvelocities are desired so as to keep equipment of a practical size,despite the large volumes of gas to be processed and the small particlesizes facilitate intimate contacting of all of the gas with bed solidsand effective use of all of the bed solids. Contactors capable of suchhigh velocities with relatively small particles and at low pressuredrops have hitherto not been described. There is, none the less, agenuine need for a fluid-solids contactor which will permit fluid-solidscontacting of small particles at high superficial gas velocities withoutsolids breakthrough or solids-entrainment. There is also a need for sucha contactor having a relatively low pressure drop and which does notencounter the problems associated with grid plugging.

DISCOVERY OF THE INVENTION

It has now been discovered that relatively small particles can becontacted with a fluid, preferably a gas, at high superficial gasvelocities with minimal gas-solids entrainment and at relatively lowpressure drops in a fluid cross-flow contactor wherein the solids arestructured or stabilized by the action of a magnetic field, saidparticles being ferromagnetic or made ferromagnetic by the inclusionwithin the particle material having this property wherein the magneticfield is transverse to the flow of fluid through the bed of solidparticles and substantially colinear with the external force field,i.e., gravity.

SUMMARY OF THE INVENTION

As one embodiment of the present invention, there is provided amagnetically stabilized fluid cross-flow bed (MSCFB), comprising:

(a) a chamber including an inlet port and an outlet port for introducingand removing a plurality of solid, discrete magnetizable particles;

(b) solenoid or magnet means for establishing magnetic field within saidchamber;

(c) a plurality of opening means in said chamber which are arranged onsubstantially opposite sides of said chamber and being situated in sucha manner as to cause the gas to flow with a velocity componentsubstantially perpendicular to the external force field (e.g., gravity)within said chamber and substantially transverse with respect to theapplied magnetic field.

The apparatus preferably includes a plenum means communicating with saidopening means on said chamber for introducing and withdrawing fluid(e.g., gas) to and from said chamber.

The chamber preferably comprises one or more upwardly extendinghorizontally or alternatively concentric spaced-apart perforateretaining means wherein the retaining means are in communication withthe respective gas inlet and gas outlet plenum.

As another embodiment of the invention, there is provided a process forcontacting a gaseous medium with a bed of solid particles utilizing themagnetically stabilized fluid cross-flow bed of the invention.

Stil another embodiment of the invention pertains to a process forremoving particulates from gaseous streams, such streams exit innitrogen oxide removal and flue gas desulfurization processes and incombined cycle power processes as hereinafter described.

The process of the invention utilizing the magnetically stabilizedcross-flow bed contactor permits gas solids contacting at relativelyhigh superficial gas velocities, e.g, gas velocities at the face of thecontacting chamber ranging from 0.5 ft./sec. up to 10 ft./sec. and more,utilizing particles having a mean diameter of 1500 microns or less andpreferably less than 1000 microns.

The primary advantages of the magnetically stabilized contactor are:

(a) No complicated and costly air distribution fluidizing grid isrequired to distribute the incoming gas within the contactor;

(b) By virtue of the compact nature of the contactor, i.e., thecontactor may be typically two to twelve inches thick (and several feedhigh, e.g., up to about 50 feet or higher, very large geometrical facesurface areas are possible within a relatively small volume pressurevessel. The action of the applied magnetic field on the magnetizableparticles also provides for orientation of the particles in the bed andenables one to control the porosity (or void fraction) in the bed (theporosity of the bed or bed voidage in the magnetically stabilizedcross-flow beds of the invention is typically 50 percent or more greaterthan the void fraction of conventional cross-flow and panel bedcontactors). As a result of the bed structuring and the attendant highvoid fraction which accrues from these magnetic interactions, thepressure drop across the magnetic particle bed is extremely low.

(c) By virtue of the structuring of the bed a higher capacity forcollecting or capturing particulates from gaseous streams, e.g., captureefficiencies of greater than 98% are possible when the bed contains upto 20-30 volume % of the captured particulates. The voidages in themagnetically stabilized cross-flow beds of the present invention aregreater than a comparable fixed bed.

(d) The action of the applied magnetic field on the magnetizableparticles permits the use of much higher superficial fluid velocitiesand permits the use of smaller particles than is practical withconventional, unstabilized cross-flow or panel bed contactors. The useof smaller particles permits better fluid-solid contacting, betterparticulate capture and greater chemical reaction rates than can beobtained with larger bed particles.

The higher voidages also permit superficial gas velocities up to 4 timesor more than similar beds not stabilized by the magnetic field atcomparable pressure drops. At the same pressure drops, the magneticallystabilized cross-flow beds of the present invention can possess 5 timesor more bed particles per unit volume of bed compared to comparablefixed beds or moving beds because of the relatively smaller particlesize which can be used. Thus, because of the smaller particle sizeswhich can be used in the contactor of the invention, the contactor cancontain a larger external surface area of particles per unit volume ofbed compared to a normal bed of the same pressure drop.

(e) The applied magnetic field on the bed of magnetizable particlesimparts an anisotropic structure to the bed which, in particulatecapture processes, increases filtering efficiency. This structuring alsoreduces the stripping of captured particles from the magnetized filtermedia.

(f) Since the contactor is in a generally upstanding vertical position,the solid magnetizable particles can be conveniently fed from the top ofthe contactor and the particles are simply withdrawn from the bottom bythe flow of gravity. The flow of the particles can be controlled by avariable opening underneath the contactor or by controlling the appliedmagnetic field. The movement of the particles can be slowed down orliterally locked in place increasing the magnetic field. Since theindividual magnetic particles can be "locked" together by theinterparticle magnetic forces generated by the external electromagnets,the particles form a continuous, but expanded element in the bed, whichcontinuously falls at a controlled rate, to the bottom of the contactorin a plug-flow fashion. The continuous nature of this contactor requiresonly one contacting vessel, in contrast to fixed bed contactors (e.g.,Squires) which require contacting swing reactor systems. The headpressure and gravity acting on the vertical columns containing themagnetized particles keeps the particles moving in a downward direction(when the magnetic field is not so high as to "lock" the particles inplace) whereupon they exit through the port of the contactor.Preferably, the magnetic particles leaving the contactor are recycledback to the contactor for reuse. In the case of catalyst particles,sorbent particles or particles having captured particulates adhering orentrapped, it is preferred to pass such spent particles through aregenerator or separator before recycling them to the contactor. Afterthe particles or catalyst particles have been cleaned or otherwiserejuvenated, they may be transported via pneumatic or other mechanicalmeans to the top of the contactor where they being their downward fallin a controlled manner into and through the contactor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 represents a vertical front cross-sectional view of themagnetically stabilized cross-flow contactor in a single stage mode.

FIG. 2 represents a left side perspective view of the magneticallystabilized cross-flow contactor of the panel bed type.

FIG. 3 represents a vertical front cross-sectional view of themagnetically stabilized cross-flow contactor of the annular type.

FIG. 4 is a vertical front cross-sectional view of the magneticallystabilized cross-flow contactor showing solids regeneration and returnof solids to the magnetically stabilized cross-flow contactor.

FIG. 5 is a vertical front cross-sectional view of the magneticallystabilized cross-flow contactor showing a dual contactor which includesthe combination of cross-flow and raining solids contacting.

FIG. 5a represents a detailed vertical front cross-sectional view of apart of the cross-flow expanded zone of FIG. 5.

FIG. 6 is a cross-sectional top elevation view of a multi-panelcontactor similar to FIGS. 1, 2 or 4.

FIG. 7 is a vertical front cross-sectional view of a concentric annulardesign for using the magnetically stabilized cross-flow contactor whichis suitable for use in flue gas desulfurization or nitrogen oxideremoval processes.

FIG. 8 is a vertical front partial cross-sectional view of themagnetically stabilized cross-flow contactor applied to a combined cyclepower process.

FIG. 9 is a vertical front cross-sectional view of the magneticallystabilized cross-flow contactor illustrating an improved louver design.

FIG. 10 is a vertical front cross-sectional view of the magneticallystabilized cross-flow contactor illustrating another louver design whichincludes bed particle support devices.

FIG. 11 graphically represents that the bed particle blow-out velocityis increased and the pressure drop resulting from a given gas flow isdecreased by increasing the applied magnetic field strength in themagnetically stabilized cross-flow contactor.

FIG. 12 graphically represents that the particulate capture efficiencyin the magnetically stabilized cross-flow contactor is improved byincreasing the applied magnetic field strength.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As indicated previously, the present invention relates to a magneticallystabilized cross-flow gas-solids contacting apparatus which includes:

(a) a chamber including an inlet port and an outlet port for introducingand removing solid, discrete magnetizable particles;

(b) a solenoid or magnet means for establishing a magnetic field withinsaid chamber; and

(c) a plurality of openings in said chamber arranged on substantiallyopposite sides of the chamber and being situated in such a manner as topermit gas to flow with a velocity component substantially perpendicularto the external force field (e.g., gravity) within said chamber andsubstantially transverse with respect to the applied magnetic field. Theopenings in the chamber are preferably encased by plenum means whichtransport the gas to and from the openings in the chamber. The plenummeans will include a gas inlet plenum communicating with the openingmeans on one side of the chamber and the other plenum, a gas outletplenum, communicates with the opening means on the opposite side of thechamber.

The chamber may be annular, or alternatively, may comprise one or morepairs of substantially upwardly extending horizontally spaced-apartperforate retaining walls, one of which is in communication with the gasinlet plenum and the other of which is in communication with the gasoutlet plenum.

The openings on the chamber will preferably include a plurality ofsupport members, each of which are adjacent to the openings and incommunication with the gas inlet plenum. The support members arearranged to extend outwardly from below their adjacent openings and intothe inlet plenum to support and expose to the chamber a plurality offree surfaces of particulate material. They are arranged cooperativelyto support the solid, discrete magnetizable particles and retain theparticles within the contacting chamber. A similar arrangement ofoutwardly extending support members, each of which are adjacent to theopenings and in communication with the gas outlet plenum, will bepositioned opposite the inlet plenum.

Both of these outward extending support members (louvers) are preferablyinclined at an upward angle to enable higher gas velocities to beemployed without blow-out of the solids. The angle of incline will vary,depending on the gas velocity, size and shape of the particles, and themagnetization of the particles (as induced by the applied magneticfield). The support members or louvers may be of special design tofacilitate air flow into and out of the chamber as well as providesupport for the magnetizable particles. For example, the support membersmay be arranged to extend outwardly and downwardly in a general curvefrom below their adjacent opening and then extend further in a generalcurve upwardly and into the chamber. The edge of such support may beeither above the inner edge of the free surface supported by the memberor, when below, a line drawn through these edges is inclined at an angleof less than about 60° to the horizontal, preferably less than 45° tothe horizontal.

The chamber most suitably comprises a plurality of perforate panelsjoined end-to-end to one another and folded back as in the pleats of anaccordian as shown in the cross-sectional top view in FIG. 6. Thisarrangement provides maximum contacting volume per unit of spacerequired for efficient contacting and also maximizes use of theelectromagnetic coils surrounding the chamber.

The thickness of the contacting chamber is preferably kept as small aspossible to minimize the pressure drop of gas passing through the bed.The thickness will be a function of the needed contact time andallowable pressure drop. Generally, the thickness of the chamberretaining the solid, discrete magnetizable, fluidizable particles willbe in the range from about 1 inch to about 2 feet, preferably from about2 to about 12 inches and, more preferably, from about 4-10 inches thick.The height of the contacting chamber may vary substantially depending onspace available, volume of gas to be processed, etc. Typically, theheight may range from 1 ft. up to as high as 80 or 100 ft. However, acommercial unit may typically be 10 to 60 ft., or 25 to 50 ft. high.

In designing the perforate chamber walls it is preferred to provide aseal zone above and below the openings in the chamber, i.e., zones whereno openings exist as shown in FIG. 4. The seal zones prevent the gasfrom leaking upward or downward within the chamber containingmagnetizable solid particles.

The magnet means for magnetizing the solid, discrete magnetizableparticles within the chamber is generated by a plurality of solenoid orelectromagnetic coils which surround the contacting chamber. The coilsare preferably arranged in such a manner that they establish a magneticfield substantially colinear with the external force field (e.g.,gravity) and substantially perpendicular to the flow of gas through thebed of magnetized solid particles. The manetic field is preferablyestablished by two or more electromagnetic coils of circular orsemi-rectangular toroidal form positioned around the outer wall of theapparatus. The magnetic field is preferably substantially uniformlyapplied to at least a portion or a zone of the chamber containing thesolid, discrete magnetizable particles. Preferably, the magnetic fieldis imposed on at least the region or regions where the openings in thevessel exist and most preferably the entire chamber. In any event, it ispreferred that the region stabilized by the applied field has avariation of its vertical magnetic component less than exceed 25% of theaverage vertical component over the region or zone of the chambercontaining the solid, discrete magnetizable particles. More preferably,the magnetic field intensity will vary no more than 10% and morepreferably no more than 5% over the stabilized region. Often, it will bedeemed desirable to design such regions or zones to have only about a 5%or less variance.

In many processes it will be desirable that the entire chamber(s) bestabilized by the magnetic field. In such cases, the entire bed ofsolids can be controlled. Thus, when the magnetic field is appliedhaving a substantial vertical component to stabilize the solids medium,the variation of the vertical component of the magnetic field to themean field in the bed should be no greater than 10%. Often, suchchambers will be designed to have less than 5% variation over the mean.Such uniform fields have the greatest tendency to form a homogeneous,yet anisotropic, bed.

The electromagnet coil may be energized by direct current (DC) oralternating current (AC); however, DC, i.e., nontime varying, verticalfields are preferred since they are able to provide a uniform field withthe lowest power requirements. If desired for special purposes, one mayemploy a spatially uniform DC field having a superposed AC component.Such an arrangement will behave substantially like a DC field if the DCfield intensity is substantially greater than the amplitude of the ACfield intensity.

The intensity of the required magnetic field will vary greatly,depending on the magnetization properties of the solid, discrete,magnetizable particles, the degree of magnetization of the particlesdesired, i.e., how fluid, stiff or locked, one wishes the particles.However, the applied magnetic field will generally range from about 25to about 1000 oersteds (2.5×10⁻⁴ to 1.0×10⁻¹ Tesla), preferably from 50to about 500 oersteds, and more preferably from 100 to about 300oersteds.

The solid, discrete, magnetizable particles to be used in the practiceof the invention are preferably particles having a low or zerocoercivity to facilitate solids handling external to the magnetizedcontacting chamber. Ferromagnetic and ferrimagnetic substances,including but not limited to magnetic Fe₃ O₄, γ-iron oxide (Fe₂ O₃)ferrites of the form XO.Fe₂ O₃, wherein X is a metal or mixture ofmetals such as Zn, Mn, Cu, etc.; ferromagnetic elements including iron,nickel, cobalt and gadolinium, alloys of ferromagnetic elements, etc.,may be used as the magnetizable solid particles. Nonmagnetic materialsmay be coated with and/or contain dispersed therein solids having thequality of ferromagnetism. For example, composites of magnetizable solidparticles prepared for use in some catalytic processes may contain from2 to 40 volume percent and preferably 5 to 20 volume percent and morepreferably 10 to 15 volume percent of the ferro- or ferrimagneticmaterial and the balance will be comprised of nonmagnetic material.Often it will be desirable to use a ferro- or ferrimagnetic compositewith a nonmagnetic catalytic material. The bed solids in the chambercontaining the magnetizable particles may also include particulatesolids which are nonmagnetizable. In other processes, for example, wherehigh magnetization is desired, it will be desirable to use 100% ferro-or ferrimagnetic solids.

The solid, discrete, magnetizable particles are most preferablycomposite magnetizable particles disclosed in any of copendingapplication Ser. Nos. 943,384; 943,385; 943,552; 943,553; or 943,554,filed Sept. 18, 1978, the disclosure of which are incorporated herein byreference. U.S. Ser. No. 943,384 to R. E. Rosensweig disclosesmagnetizable compositions comprising geometrically elongate particlesconstituted of composites of nonferromagnetic solids and elongateferromagnetic inclusions, particularly compositions wherein theinclusions are parallelly aligned in the direction of the major axis ofthe particle. These particles preferably have high L/D ratio, i.e., atleast 2:1, and preferably 4:1 and more preferably 10:1 and more. Theseelongated particles have demagnetization coefficients significantly lessthan 1/3. These elongated particles are capable of aligning along thelines of the magnetic field in a more oriented manner than sphericalparticles. U.S. Ser. Nos. 943,385 and 943,554 disclose a method forparallelly aligning orienting elongate ferromagnetic inclusions in anadmixture of a hydrogel precursor and said elongate inclusions prior togelation, and maintaining such alignment or orientation of theferromagnetic particles during gelation which takes place in a hot oilbath. U.S. Ser. No. 943,552, discloses (i) particulate admixtures ofnonferromagnetic solids and elongate ferromagnetic solids: (ii)composites comprising particulates constituted of nonferromagneticsolids and a single elongate ferromagnetic inclusion; (iii) compositescomprising particulates constituted of nonferromagnetic solids and aplurality of elongate ferromagnetic inclusions wherein the long sides ofthe inclusions are parallelly aligned and (iv) processes of using any of(i), (ii) or (iii) for fluids-solids contacting. U.S. Ser. No. 943,553discloses composite particles constituted of nonferromagnetic solids anda plurality of elongate ferromagnetic inclusions randomly aligned aswell as process for using the compositions for fluid-solids contacting.

In processes where very high temperatures will be encountered, it ispreferred that materials having a high Curie point be employed. Examplesof such materials useful for this purpose are disclosed in U.S. Ser. No.000,384, filed Dec. 29, 1978 to R. C. Krutenat and Chih-an Liu, thedisclosure of which is incorporated herein by reference. In thisapplication, a base magnetic metal such as iron or cobalt is alloyedwith aluminum, chromium, silicon or combinations of these materials (andoptionally, Y, Hf, Zr or La can be incorporated) and air oxidized atelevated temperatures.

Generally speaking the size of the solid, discrete magnetizableparticles will be such that their mean diameter ranges from about 100 toabout 1500 microns, preferably from 150 to about 1000 microns and morepreferably from about 250 to about 500 microns. The particle size rangereferred to herein is that determined by the mesh openings of a firstsieve through which particles pass and a second sieve on which theparticles are retained.

The solid, discrete magnetizable fluidizable particles may be admixedwith nonmagnetic materials. For example, silica, alumina, metals, e.g.,copper and salts thereof, catalysts, coal, etc., may be admixed with themagnetizable particles and the advantages of the present invention stillobtained. In the case of admixtures (as opposed to composite materialscontaining the magnetizable particles) it is preferred that the volumefraction of magnetizable particles exceed 75 percent, or preferablyexceed 90 volume percent of the total particles. Normally the bed willbe composed of 100 volume percent of the magnetizable particles (i.e.,it will not contain admixtures of other materials). When thenonmagnetizable admixtures exceed 25 volume percent, the particlemixtures may separate analogous to liquids of limited solubility.

An important factor in selecting or preparing the solid magnetizable,particles is the magnetization M of the particle. The higher themagnetization, M, of the particle, the higher the superficial fluidvelocity and the better the contacting the particulate captureefficiency, etc., at which one may operate the contacting device of theinvention without blowout or entrainment of solids by the crossflowinggas stream, all other factors such as particle size and distributionbeing held constant. The magnetization of the solid, discretemagnetizable particles in the bed without the contacting chamber willhave a magnetization M of at least 10 gauss. Generally, for high fluidvelocities the particles will have a magnetization, as being imparted bythe applied magnetic field, of at least 50 gauss, preferably at least100 gauss and more preferably at least about 150 gauss, e.g., 150-400gauss. For those processes requiring very high fluid velocities, themagnetization of the particles may be up to about 1000 gauss or more. Insome instances it will be desired to create a degree of magnetization onthe particles such that they form a stiff mass or lock-up within thecontactor vessel, rather than allow the particles to flow in a downwardmotion by the action of gravity. It will be realized that one aspect ofthe instant invention pertains to controlling the rate of descent of theparticles simply by the application of the applied magnetic field. Thus,the applied magnetic field can control the rate of flow of theparticles, the voidages in the bed, the gas velocities at which thesystem one can operate and the relative efficiency of the gas-solidscontacting process.

The magnetization, M, of the particles, as is wellknown, is defined asB-H in the particle, where B is the magnetic induction and H is themagnetic field, the fields being defined in standard published works inelectromagnetism, e.g., Electromagnetic Theory, J. A. Stratton,McGraw-Hill (1941). The value of M may be measured in a variety of ways,all of which give the same value M since M has an objective reality.

One means for determining magnetization M of the particles in a bedunder the influence of a given applied magnetic-field is to measuretheir magnetic moment at that field in a vibrating sample magnetometerunder conditions of similar voidage, sample geometry and temperatures asexist in the process to be used. The magnetometer gives a value of σ,the magnetic moment per gram from which magnetization M is obtained fromthe formula:

    M=4πσ

where ρ is the density of the particles in the test samples, σ is themagnetic moment in emu/gm (electromagnetic units per gram), M is themagnetization of the particles in gauss at the applied magnetic fieldused in the test and π is 3.1416 . . . a well-known physical constant.

The actual magnetization of the particles in the contacting chamber willbe a function of the particles themselves (i.e., the degree ofmagnetizability they inherently possess) and the intensity of theapplied magnetic field. It is to be understood that the term "appliedmagnetic field" used throughout the specification and claims refers toan empty chamber or vessel applied magnetic field.

As stated above the magnetizable particles should have a certain degreeof magnetization M which is imparted to the particles by the intensityof the applied magnetic field. Obviously one would seek the lowestapplied magnetic field possible because of cost. Commonly, many of thecomposite particles referred to in the above-mentioned patentapplications will require at least 50 oersteds, more often more than 100and preferably less than 1000 oersteds applied magnetic field to achievethe requisite magnetization M. The determination of the applied magneticfield will take into account the type of particles employed, i.e., theirmagnetization, particles size and distribution, the superficial fluidvelocity to be used, etc.

Generally, the magnetization M of a particle as obtained from amagnetometer when a given magnetizing field H_(a) is applied will notprovide a value which is the same as the magnetization of the particlein response to the same intensity of magnetic field in the contactingchamber to be used in accordance with the teachings of the presentinvention.

The purpose of the following is to indicate a method for determining themagnetization M_(p) of a typical particle in a bed from those valuesobtained from a magnetometer. Generally, this will require a calculationsince the effective field that a bed particle is subjected to depends onthe applied field, the bed geometry, the particle geometry, the bedvoidage and particle magnetization. A general expression has beenderived to relate these quantities based on the classical approximationof the Lorentz cavity that is employed in analogous physical problemssuch as the polarization of dielectric molecules.

    H.sub.a =H.sub.e +M.sub.p [d.sub.p +(1-ε.sub.o)(d.sub.b -1/3)](1)

H_(a) is the applied magnetic field as measured in the absence of theparticles, H_(e) the magnetic field within a particle, M_(p) theparticle magnetization, d_(p) the particle demagnetization coefficient,ε_(o) the voidage in the bed, and d_(b) the bed demagnetizationcoefficient. The term -1/3 is due to the magnetizing influence of a(virtual) sphere surrounding the bed particle.

The expression above applies as well to a sample of particles such asused in a magnetometer measurement. In that case d_(b) is thedemagnetization coefficient d_(s) corresponding to shape of the cavityin the sample holder.

Magnetometer measurement produces a graph of M_(p) vs. H_(a). Using theabove equation and known values of d_(p), d_(s), ε_(o), M_(p) and H_(a)a corresponding value of H_(e) may be computed. When the value of H_(e)is small its value found in this manner is determined by a differencebetween large numbers, hence is subject to cumulative errors.Accordingly, a modified approach is useful as described in thefollowing.

Thus, it is useful to define a reference quantity H_(s) representing thecalculated field in a spherical cavity at the location of the particle.It is imagined that the magnetization of surrounding particles isunchanged when the said particle is removed.

    H.sub.s =H.sub.a -M.sub.p [(1-ε.sub.o)(d.sub.b -1/3)](2)

Combining the two expressions gives an alternate relationship for H_(s),in which H_(a) is eliminated.

    H.sub.s =H.sub.e +Mpd.sub.p                                (3)

The expression is recognized to give H_(s) as the change of field inpassing from the inside of a particle to the outside of the particle.

Denoting K_(m) as the following constant

    K.sub.m =1/(1-ε.sub.o)(d.sub.s -1/3)               (4)

then from (2) K_(m) equals the quantity M_(p) /(H_(a) -H_(s)) i.e.,

    K.sub.m =M.sub.p /H.sub.a -H.sub.s                         (5)

Thus, on the graph of M_(p) vs. H_(a) straight lines of slope K_(m)intersecting the measured curve and the H_(a) axis relate correspondingvalues of M_(p) and H_(s). For example, when the sample is contained ina spherical cavity, d_(s) =1/3, K_(m) is infinite and H_(s) equalsH_(a). For a long sample such that d_(s) =O, K_(m) is negative and H_(a)is less than H_(s) i.e., the field magnetizing a particle of the sampleis greater than the field applied to the sample.

Additionally, for a process bed, a constant K_(p) may be defined asfollows:

    K.sub.p =1/[(1-ε.sub.o)(d.sub.b -1/3)]             (6)

It may also be seen from Eq. (2) that a line of slope--K_(p) passingthrough a point H_(a) on the horizontal axis of the graph of M_(p) vs.H_(s) intersects the curve on the graph at a value of M_(p) giving theparticle magnetization in the bed. Thus, the particle magnetizationM_(p) in a process bed has been related to the field H_(a) applied tothe process bed.

The relationship of Eq. (1) is an approximation which is more accuratefor beds having high voidage than for very densely packed samples.

The superficial fluid velocity employed in operating the magneticallystabilized cross-flow contactor may be regulated to vary over a widerange of superficial fluid velocities. However, the superficial fluidvelocity should be insufficient to cause substantial entrainment of thesmaller bed particles in the exit gas stream or insufficient to cause"solids blow-out". Solids blow-out occurs at a relatively lowsuperficial fluid velocity in unstabilized cross-flow contactors. Theapplication of the magnetic field, in the case of the magneticallystabilized cross-flow contactor, enables one to use substantially highersuperficial fluid velocities before substantial solids entrainment orsolids blow-out. The superficial fluid velocity sufficient to causesubstantial entrainment of the smaller bed particles in the exit gasstream may be insufficient to cause "solids blow-out". The superficialfluid velocity sufficient to cause solids blow-out is the superficialfluid velocity at which the solids suddenly (catastrophically) exitthrough the gas exit openings of the contactor. This occurs when theaerodynamic drag on the bed by the gas flow exceeds the retaining forceswhich derive from the particle-to-particle coupling due to the magneticfield and from the physical barrier provided by the gas exit openings'inner surfaces. Thus, the magnetization of the particles in the bed andthe size of the gas exit openings are interrelated in determining themaximum superficial fluid velocity that can be tolerated before solidsblow-out occurs. Unlike the unstabilized cross-flow contactors of theprior art, the blow-out superficial fluid velocity in the case of theinstant magnetically stabilized cross-flow contactor can be controlledby appropriate magnetization of the particles (e.g., by increasing theapplied magnetic field).

While not wishing to be bound by any theory, the blow-out velocity maybe represented in the following terms at blow-out:

(1) Drag Force=K₁ (weight)+K₂ (magnetic force)

(2) C(A_(p))ρ_(f) U² /2 g_(c) =K₁ (Vol. P)ρ_(p) +K₂ (M_(p))(Vol. P.)

Where: A_(p) =πD_(p) /4=drag area of the particle

Vol. P.=πD_(p) ³ /6=volume of particle

D_(p) =Diameter of particle

ρ_(p) =Density of particle

M_(p) =Magnetization of particle

U=Gas velocity through louvers

ρ_(f) =Density of fluid (gas)

μ_(f) =Viscosity of fluid (gas)

g_(c) =Gravitational constant

K₁,K₂ =Constants fixed by bed enclosure design, e.g., louver spacing

C=f(Re) and for 2<Re<500

    =18.5(μ.sub.f /D.sub.p Uρ.sub.f)

solving (2<Re<500):

    U=K.sub.3 D.sub.p.sup.1.14 (K.sub.1 ρ.sub.p +K.sub.2 M.sub.p)0.714

Where: ##EQU1##

Typically, by use of magnetizable particles having an average meandiameter of 300 microns, a contactor 1-12 inches thick having gas exitopenings of 3/4 inches and an applied magnetic field ranging up to 1000oersteds, the superficial fluid velocity at the face of the contactormay be as high as 10 ft./sec. (i.e., 300 cm./sec.). Generally, thesuperficial fluid velocity at which blow-out will occur will to 6ft./sec. and more often 1.5 ft./sec. to 4.5 ft./sec.

The pressure drops encountered by operating the contactor of theinvention is generally quite low. It will generally be less than 2-3inches/inch of bed, more preferably less than 1-2 inches/inch of bed.

DETAILED DESCRIPTION OF THE DRAWINGS

In the several figures, the like reference numerals refer to like partshaving like functions. In FIG. 1 the magnetically stabilized cross-flowcontactor comprises a casing 1 (preferably nonmagnetic, not shown) and acontacting chamber 2 (preferably nonmagnetic) which contains a pluralityof solid discrete magnetizable particles 6. The particles are suppliedto chamber 2 via port 14 and exit chamber 2 via port 16. The particlesare magnetized by magnet means 4 comprising a plurality ofelectromagnetic or solenoid coils coaxially surrounding chamber 2. Thesecoils may be energized by DC or AC current. It is preferred to employnontime varying fields colinear to the external field (i.e., gravity).Direct current (DC) rather than alternating current (AC) is preferred toenergize the electromagnetic coils because it requires less power thanthe AC energized electromagnetic coils. The gas to be treated from anysuitable source (not shown) flows through conduit 10 (not shown) andinto chamber 2 via a plurality of openings 8. The gas passes through themagnetized particles 6 in a generally cross-flow manner (i.e.,perpendicular to gravity and the applied magnetic field) and exits thechamber 2 through a plurality of openings 9. The processed gas may thenbe transported from the contactor via conduit 12 (not shown).

FIG. 2 is a left-side perspective view of the magnetically stabilizedcross-flow contactor as shown in FIG. 1, which additionally includes aplurality of panel type louvers for the entry and exit of the gases tobe contacted in the contactor. As shown, the solids 6 enter at 14 intocontactor 2. The bed of magnetizable particles 6 moves down through thecontactor 2 in a controlled manner while under the influence of themagnetic field 4a created by the magnet means (not shown). The gas froma suitable source, not shown, enters an inlet means 10, not shown, andpasses by the panel louvers 8a into the openings 8 into the contactor 2.The gas exits through the openings 9 and the solids particles areretained in contactor by the action of the magnetic field and theupwardly extending panelled louvers 9a, whereupon the gas is withdrawnvia gas outlet 12 (not shown).

FIG. 3 is a cross-sectional view of the right half of an annular designusing the cross-flow contactor of FIG. 1, which additionally includesinlet 18 and outlet 20 plenums for the contactor. FIG. 3 also shows aplurality of panelled louvers each adjacent the openings means 8 and 9in communication with the gas inlet plenum 18 and gas outlet plenum 20.These louvers are arranged to extend outwardly from below their adjacentopenings and into the inlet or outlet plenums to expose to thecontacting chamber a plurality of free surfaces of the solid particles.The panelled louvers are arranged cooperatively to support the solid,discrete, magnetizable particles and retain the particles within thecontacting chamber 2. The upward angle of the support members willpreferably be adjusted based on the angle of repose of the magnetizedparticles within the contactor 2. Obviously, this will depend on thesize and shape of the particles, the degree in which they aremagnetized, the size of the openings 9 and the superficial velocity ofthe gas passing through the contactor 2.

FIG. 4 illustrates a cross-sectional view of another embodiment of theinvention as shown in FIGS. 1, 2 and 3. In FIG. 4 it is shown that thegas to be contacted enters port 10 whereupon it enters into a commoninlet plenum 18. The gas from plenum 18 then enters the openings 8 inthe pair of substantially upwardly extending horizontally spaced-apartperforate retaining walls into the contacting zone 2, whereupon the gasexits through opening means 9 into the outlet plenum 20. Adjacent to theopenings 8 and 9 are louvers 8a and 9a. The effluent gas from the outletplenum 20 then is suitably transported from the contactor via port 12.The magnetizable particles 6 pass downwardly through the contactingvessel 2 first passing through a seal zone 36 which acts to prevent gasfrom leaking upward into vessel 2 and then into cross-flow zone 34. Theporosity or voidage in the bed, the velocity of descent of the particlesand the relative magnetization M of the particles themselves iscontrolled by the applied magnetic field from the magnet means 4coaxially surrounding the vessel 1. The magnetizable particles may becaused to move downward in a continuous, semicontinuous or batch-wisemanner simply by the control of the valve means above and below vessel 1designated as valve 32 and valve 22. The valve means may be any suitablevalve, but may include an electromagnetic valve such as disclosed inU.S. Pat. No. 3,067,131 to Bergstrom. The angle of the exit region 16 ofthe contacting vessel 1 is such that the magnetizable particles do notsubstantially stick to the sides of the vessel as they flow downward. Asshown in FIG. 4, the particles suitably pass through valve 22 intoconduit 24 whereupon they are preferably passed through a solidsregenerator 28. From time to time solids may leak from louvers 9a intooutlet plenum 20 and these solids are suitably removed by conduit 26into conduit 24 for further processing. The regenerated solids fromsolids regenerator 28 may then be recycled to contactor 2 via valve 32and conduit 14.

FIG. 5 illustrates a combination cross-flow (radial flow)--rainingsolids contactor for countercurrent contacting of gas and solids whichalso has the capacity of removing particulates entrained in a gaseousstream in an expanded dense bed cross-flow region 34a. The contactor ofFIG. 5 possesses a raining solids reactor/contactor zone 36a. Thecontactor/reactor scheme shown in FIG. 5 is a cross-sectional schematicrepresentation of a contactor/reactor and process for carrying outsimultaneously sulfur oxide and particulate removal using a magneticsulfur oxide absorbent.

Referring to FIG. 5, the gas to be processed, e.g., a flue gascontaining sulfur oxides, nitrogen oxides and entrained particulatesenters gas inlet 10 and into plenum 18 at the bottom of the contactor.Ammonia and air are injected into the gas stream to convert the nitrogenoxides to nitrogen and water. The flue gas enters on the inside of anannular conic section 18. The dirty flue gas passes in a cross-flow orradially through the annular section 2a through openings 8 having louvermeans 8a and out of openings 9 past louver means 9a and the cleanedgases then pass into a plenum chamber 20. The contactor is coaxiallysurrounded by electromagnetic coils 4. The magnetic sorbent particles 6flow in a downward direction by the action of gravity and into theradial flow expanded zone 34a. The particles are preferably in astiffened and expanded state by the action of the magnetic fieldgenerated by the electromagnetic coils. FIG. 5a illustrates a blown-upview of a portion of contactor 2a. The void fraction in the annularspace 2a can be adjusted from approximately 0.35 to 0.7 depending uponthe magnetic field strength of the electromagnetic coils and thecross-flow superficial gas velocity. The thickness of the annular zone2a is designed to give the filtering efficiency and pressure droprequired to remove 90-99 % of the particulate matter entrained in thegas stream. From radial expanded zone 34a the gas in plenum 20 entersthe raining solids zone 36a and the cross-flow transition zone 35. Afixed interface 35a is maintained between the raining solids zone 36aand the radial flow expanded zone 34a. At the interface the magneticsolids have a tendency to form treelike structures which collapse andform a greatly expanded stiff bed which gives a very low pressure drop.The void fraction is controlled by the magnetic field at the interface.By varying the magnetic field from electromagnetic coils 4 and 4b indifferent regions, one is able to control the void fraction in radialflow expanded zone 34a.

The partially processed flue gas from plenum 20 then flowscountercurrent to the falling solids 6 in the raining solids zone ofcontactor 54. This mode of processing provides an efficient cleanup ofthe flue gas. Simultaneously very fine particulates which escape throughthe cross-flow capture zone are captured by the failing magnetizableparticles which have been electrostatically charged by electrostaticmeans 52 powered by a suitable power source 50 prior to entering theraining solids zone 36a. The processed flue gas then leaves the rainingsolids zone to the stack via port 12.

Still referring to FIG. 5, the solids are continuously removed from thecross-flow zone via conduit 24 to maintain the interface between the twozones. The spent adsorbent particles containing fly ash are transportedto the fly ash removal zone 28 where the fly ash is removed from theadsorbent particles. The fly ash is removed from the fly ash removalzone via port 28a. In the fly ash removal zone the fly ash may beremoved from the magnetizable particles by various techniques such aselutriation, screening, magnetic separation, etc. The fly ash-freemagnetizable particles are then transported to a countercurrentregenerator 36 optionally stabilized by electromagnetic coils 4a wherethe adsorbent is regenerated with a reducing gas supplied from conduit37.

The magnetically doped particles comprises copper on magnesiumoxide-stabilized Al₂ O₃. A typical magnetic absorbent is prepared byencasing magnetic particles such as 410 stainless steel withincopper-impregnated alumina. These particles will have a particle size of10-100 μm size range. Since the sorption reaction is diffusioncontrolled, advantages are seen when the copper sorbent is impregnatedon an alumina which has approximately 50% of its pore volume inpores >1000 A diameter. The flue gas desulfurization catalyst particlesmay be regenerated by treatment in a steam and hydrogen atmosphere wherethe absorbed CuSO₄ resulting from the SO₂ absorption is converted to Cu,water and SO₂. The regenerator possesses electromagnetic field coils 4ato optionally impose a magnetic field within the regenerator. Theconcentrated SO₂ effluent from the regenerator is removed by conduit 39for further processing, e.g., conversion to sulfur. The regeneratedmagnetizable catalyst particles are then returned to the top of theraining solids zone 54 via conduit 14 in a controlled manner by valve14a where they are electrostatically charged for removing fineparticulates entrained in the incoming gas. The electromagnetic fieldcoil 4b which is coaxially positioned around the raining solids zoneinsures uniform distribution of the solids across the raining solidszone.

In order to enhance the effectiveness of particulate solids from theregenerator, it may be desirable to slightly cool the solids so that thesolids are heated by the incoming hot flue gases as they fall throughthe raining solids zone. Thermal gradients increase the ability of themagnetizable articles to capture the very fine particulates. Thefollowing represents typical operating conditions for conducting theflue gas desulfurization process using the apparatus as particularlyshown in FIG. 5.

    ______________________________________                                        Contactor Temp., °F.                                                                           650-850                                               Contactor ΔP, inches H.sub.2 O                                                                  20-60                                                 Cross-flow contactor thickness,                                                                       0.3-3.0                                               ft.                                                                           Cross-flow superficial force                                                  vel., ft./sec.          1-6                                                   Raining solids vel., ft./sec.                                                                         15-60                                                 Sorbent particle size, micron                                                                         200-1000                                              Sorbent Ferromagnetic, Wt. %                                                                          10-75                                                 ______________________________________                                    

The contactor system of FIG. 5 which has been described specifically forflue gas desulfurization can be used for a plurality of other operationswhere it is desirable to use a combination of long and short contacttime with catalytic solids. Also, heating and cooling can be carried outin the cross-flow and raining solids zones, respectively. In addition,it is possible to carry out two reactions in the contactor of FIG. 5,i.e., one in the dense, cross-flow zone and the other in the rainingsolids zone.

FIG. 6 is a top elevational view of a multipanel bed contactor useful inthe practice of the invention. It can be seen in FIG. 6 that the panels2 are arranged like the pleats of an accordion. The gas to be contactedenters into plenum 18 and passes through a plurality of panels 2containing the magnetizable particles 6 and into outlet plenum 20. Thepanels are encased by casing 1 comprised of a gas inlet duct incommunication with plenum 18 and a gas outlet duct in communication withplenum 20. Electromagnetic coils 4 coaxially encase the unit so as toproduce a substantially uniform magnetic field. The gas treatingcapacity of the arrangement illustrated in FIG. 6 can be extremely high,particularly in the case of tall panel beds. For example, panel bedsarranged in this manner can be from 10 to 60 feet in height and occupy aspace of 2 to 12 inches, preferably 6 to 10 inches wide. It will beappreciated by those skilled in the art that if one operated at a facevelocity of greater than 1 ft./sec. extremely high contacting per unitvolume can be realized by use of this contactor.

FIG. 7 is a front cross-sectional schematic view view of a cross-flow orpanel bed contactor 1. This contactor is suitable for use in a flue gasdesulfurization process and other chemical conversions. In a flue gasprocess the flue gas can typically enter into gas inlet plenum 18. Theflue gas can then be processed by passing in a crossflow manner into themagnetically stabilized cross-flow bed 2 through openings 8 containingthe magnetizable particles 6 which are capable of absorbing SO₂. Theclean flue gas leaves the bed of magnetizable particles through openings9 and into outlet plenum 20 and outlet port 12. The spent magnetizableparticles 6 in bed 2 are transported downward through the contactor 2 ina controlled manner via valve 22. The voidages in contactor 2 and thedegree in which the particles are magnetized are controlled by theapplied magnetic field from the magnet means 4. The magnetic field alsoprevents gas entrainment and blowout of the solids. The spentmagnetizable particles are removed from the contactor 2 via conduit 16through valve 22 and into separator 28, e.g., a fly ash vibrating screen29. The separated fly-ash 29a can be removed by exit port 28a and theseparated particles can be moved pneumatically through conduit 30 to thesorbent regenerator 36 via conduits 34 and 38 and returned to conduit30. Treatment in the regenerator is the same as described for FIG. 5.The regenerated magnetizable particles may be used in processing freshflue gas by control of valve 32 and allowing the particles to betransported through conduit 14 into vessel 1.

As a specific embodiment of FIG. 7, the cylindrical steel pressurevessel 1 is comprised of hemispherical heads in which there arecontained three concentric chambers of 10, 11 and 15 feet averagediameters and 20 feet high for a total area of 2240 square feet. Thechambers are formed by perforated pipes, or pipe stubs attached towoven, nonmagnetic stainless steel cloth, and contain the magneticparticles which may vary in size from 200 to 750 microns. The magneticparticles 6 are of high surface area material and contain a suitablecatalyst for the absorption of SO₂. This magnetizable catalyst may be410 stainless steel particles coated with alumina which contains copper.The SO₂ in the flue gas is reacted with the copper and oxygen from theflue gas to form copper sulfate.

The magnetic catalyst particles, which fall vertically, in the annulargaps between adjacent perforated pipes, are maintained in an expanded,but packed, configuration by a series of magnetic coils 4 which arestacked upon each other and separated by a reasonable distance. Thehighly expended bed of magnetic particles should be controlled toprovide a voidage fraction of 0.35-0.7, the control being made by theapplied magnetic field and the gas flow rate. Since the magneticparticles are essentially "locked" to each adjacent particle by theinter-particle magnetic forces, the moving bed of particles resembles acontinuous mechanical filter of adjustable voidage or porosity. The headpressure acting on the vertical columns of magnetic particles keep theparticles in a downward direction to a vibrating, or oscillating screenseparator 28. The particulates which have been captured by the magneticparticles are mechanically separated in separator 28. Theparticulate-free magnetic catalyst particles are then preferably treatedin the catalyst regenerator 36 with steam, CO and hydrogen where theCuSO₄ is converted to CuO and SO₂. After the magnetic catalyst particlesare rejuvenated they are transported via pneumatic means in conduit 30to the top of the contactor via conduit 14 where they begin theirdownward fall, in a controlled manner, through the annular gaps whichexist between the three different pipe pairs.

Operating conditions in one example using the magnetically stabilizedcross-flow contactor of FIG. 7 are as follows:

    ______________________________________                                        Flue gas flow rate:                                                                             15 × 10.sup.6 SCFH                                    Bed thickness:    16 cm.                                                      Bed particle size:                                                                              300 microns (average dia.)                                  Particle sphericity:                                                                            1.0 (sphere)                                                Bed voidage (expanded                                                         and magnetically                                                              locked-up):       0.62                                                        Gas viscosity:    1.8 × 10.sup.-4 g./cm.sec.                            Reactor pressure: Nominally 1 Atm.                                            Particle Reynolds number:                                                                       <20                                                         V.sub.o :         1.86 ft./sec.                                               ΔP:         17 cm. H.sub.2 O                                            ______________________________________                                    

The pressure drop can be estimated from the following Ergun fluiddynamics relationship for pressure drops in packed beds: ##EQU2##

FIG. 8 illustrates a partial cross-sectional frontal view and schematicprocess description of using the magnetically stabilized cross-flow bedcontactor in a combined cycle power system. In such a process as shownin FIG. 8, coal is transported to a fluid bed combustor 40. The flue gasfrom the fluid bed combustor is passed into the magnetically stabilizedcross-flow contactor via conduit 10 into plenum 18 through themagnetized particles 6 and then into plenum 20. The clean flue gas fromplenum 20 exits through conduit 12 into the turbine/generator 42 (whichalso supplies the power to run compressor 44). Air is supplied to thefluid bed combustor through conduit 46 from compressor 44. The spentsolid particles from the magnetically stabilized cross-flow contactorare transported through conduit 16 into separator 28 whereupon they arerecycled to the contactor via conduit 30. The concentrated effluent fromthe elutriator is then further processed in cyclone 36 to removeparticulates. Typical conditions for the process include processing aflue gas of 1500°-1700° F. and at pressures of 5-20 atmospheres. Theflue gas contains about 1-20 grs/SCF of fly ash.

FIG. 9 illustrates an improved louver design of the magneticallystabilized cross-flow contactors similar to those shown in FIGS. 1 to 7.In particular, a " "-shaped inlet louver 8b is shown where the louverextending from the contactor extends outward and upwards into plenum 18at an angle greater than about 45° to the horizontal and a portion(preferably about one-half) of the louver extends further outward anddownward at an angle greater than 45° to the horizontal. This improvedlouver design is particularly useful when removing particulates with themagnetically stabilized cross-flow bed where uniform distribution of thegas to the moving magnetically stabilized bed, the prevention ofplugging, and the achievement of very low pressure drops over the entirereactor section are desirable. Ordinarily, large particulate materialsentering the bed will blind or increase the pressure drop on the inletface of the moving column of solids within the louvers of the type shownin FIGS. 2-5. It is desirable to remove as much particulate material aspossible before the particulate laden gas reaches the moving column ofsolids. This can be achieved by using the -shaped inlet louvers whichcauses the gas to make a very abrupt change in path. This causes theheavy particulates to drop out of the gas and they are collected in thelower part of the inlet plenum 18. The ash from plenum 18 is removed byconduit 26. The superficial gas velocity in the inlet of the -shapedlouvers may range from about 2 to 15 ft./sec., the actual velocitychosen will depend upon the nature of the particulate capturing solidand the applied magnetic field.

FIG. 10 illustrates another improved design of the magneticallystabilized cross-flow contactor. In particular, support means 11 (e.g.,rods, angle irons, vertical bars, incline bars, rods on a triangularpitch, etc.) are placed near the inlet and outlet louvers and extendinto the contactor containing the magnetizable solids. By properplacement of the support devices near the louver inlets and outlets,stabilization of the solids can be increased in these areas. Also, whenthe supports are placed in this position, the distance between thelouvers can be increased substantially. This improved design isparticularly useful where large panels ranging from 10 to 50 feet highand 4 to 12 inches thick will be employed. Such panel contactors willrequire the use of a very high column of solids moving down the panelwhich will generate a considerable pressure head and weight on thelouvered paneled section. By use of the support means 11 shown in FIG.10 higher gas velocities and improved solids flow can be obtained in themagnetically stabilized cross-flow beds. The support means willstabilize the solids flow and support part of the weight of the movingsolids in the contactor. The support means may be ferromagnetic, weaklyferromagnetic or nonferromagnetic.

The following examples serve to more fully describe the manner of makingand using the above-described invention, as well as to set forth thebest modes contemplated for carrying out various aspects of theinvention. It is understood that these examples in no way serve to limitthe true scope of this invention, but rather are presented forillustrative purposes.

It will be understood that all proportions are in parts by weight,unless otherwise indicated.

EXAMPLE 1

This example illustrates that one can operate at substantially highersuperficial gas velocities before blowout by use of small magnetizablesolids in a magnetically stabilized gas cross-flow contactor.

The contactor consists of an upstanding rectangular plexiglass containersimilar to that shown in FIG. 2. The contactor is 17 inches high, 8inches thick in the direction of gas flow and 1 inch wide. The contactorcontains six louvered openings on the lower 4 9/16 inch portion of thecontactor. The louvers are set at 45° to the horizontal spaced 3/4"center to center measured vertically. The plexiglass louvers are about1.4 inches long in the direction of the gas flow and 1/16 inch thick.After filling solids container 2 with the magnetizable solids it wassealed at the top and bottom. Each face of the contactor formed by thelouvers is encased with plenum means 18 and 20, one of which isconnected to a gas inlet source and the other means for withdrawing thegas. Pressure drop measurements were taken from the pressure tapsattached to the inlet and outlet plenums at the center of each of thelouver spaces.

The contactor was placed within ten magnetic coils stacked on top ofeach other having an internal diameter of 15.7 inches, an outer diameterof 25.3 inches and about 22 inches in height. Each coil had 270 turns ofa conductor 1 inch high×0.025 inch thick and insulated with 2 mill Mylar1 inch wide between turns. Six mills of Mylar was positioned between thesolenoid coil section and support plate. The inductance was 18.1 mH(with air core) and a resistance of 0.296 ohms. The coils were placed ina support structure. At 15 amps exitation 485 oersteds could be obtainedand the oersteds/amp at the solenoid center was 32 oersteds. Each coilwas separately energized with DC current (from Gates Model No. GT 14.15,manufactured by Gates Electronic Company, Inc., New York, N.Y.) toprovide a uniform magnetic field in the contactor.

The solids container of the contactor was filled to the top withmagnetizable solid particles comprising 40 micron 410 stainless steelparticles encased in Al₂ O₃, the composite having an average meandiameter of about 900 microns. Air was metered into the inlet plenum andallowed to exit the outlet plenum. Pressure drop measurements were takenat various levels of superficial gas velocities. The air supply wasincreased starting at zero magnetic field until blow-out of solidsoccurred. Blow-out velocity was noted at the superficial gas velocity atwhich the magnetizable beads began to continuously fall into the outletplenum. Data were taken at zero, 165 and 320 oersteds applied magneticfield. The results of the experiments are shown in FIG. 11. As shown,solids blow-out occurred at less than 40 cm./sec. superficial gasvelocity with no field, whereas superficial gas velocities greater than65 cm./sec. and 100 cm./sec. were obtainable at 165 and 320 oersteds,respectively. Also, it can be seen from FIG. 11 that, at comparablesuperficial gas velocities, the pressure drop (cm. H.sub. 2 O/cm.bed)decreased as the applied magnetic field was increased, e.g., over a 50%reduction in pressure drop.

EXAMPLE 2

This example further illustrates that higher gas velocities, beforesolids blow-out, can be practiced by use of the magnetically stabilizedgas cross-flow contactor than with an unstabilized gas cross-flowcontactor. In this example three different contactors having threedifferent louver angles were used. Except for the angle of the louvers,the contactors were similar to the one shown in FIG. 2. Each of thecontactors were 311/4 inches high, 3 15/16 inches thick in the directionof the gas flow and 1 7/16 inches wide. The contactors having louvers 8aand 9a at angles of 30° and 45° to the horizontal (the louvers werespaced 3/4 inch center to center measured vertically) had six openings.The contactor with 60° angle louvers had four louvers (with threeopenings) on each side of the contactor. The louvers in each of thethree contactors was 1.4 inches long in the direction of gas flow and1/16 inch thick. The open face provided by these louver arrangements was43/8 inches high in each of the three contactors. Inlet and outlet gasplenum 18 and 20 walls were spaced about 3/4 inch from the outer edge ofthe louvers and 11/4 inch from the solids retaining wall of thecontactor. Pressure taps were located approximately central to thelouver openings in the inlet and outlet plenums.

Tests were made using two magnetic modules for applying a field to thethree contactors described above. With reference to Table I the firsteight tests listed involved the use of the same field generating coilwhich was used in the tests involved in Example 1. The remaining sixteentests listed in Table I utilized, for magnetic field excitation, asingle solenoid winding 16.75 inches in height and comprising 16 layersof 119 turns per layer, said turns being made with No. 8 square copperwire encased in varnish impregnated insulation. The windings wereconnected in series-parallel combination to permit excitation by adirect current power supply having an output rating of 50 ampere maximumand 50 volts maximum. The solenoid was wound on an aluminum spool havingan internal diameter of 7.75 inches.

Several blow-out velocity tests were carried out as in Eample 1, i.e.,placing each of the three contactors within above-described magnetmodules and introducing air into the filled contactors. The followingtable illustrates the results of these tests which show the blow-outvelocity for each of the three above-described contactors at differentfield strengths and particle compositions. As seen from the data in thetable, the superficial velocity (both at the face of the louver and inthe bed) before solids blow-out (as defined in Example 1) increases withincreasing magnetic field strength.

                  TABLE I                                                         ______________________________________                                        BLOW-OUT VELOCITY DATA                                                               Material                 Blow-out Velocity,                            Louver (average particle                                                                              Field,  Ft./Sec.                                      Angle  diameter)        Oe      Louvers                                                                              Bed                                    ______________________________________                                        30°                                                                           Nalco.sup.1 (950 μm)                                                                        480     2.70   2.40                                   30°                                                                           Marumerized.sup.2 (911 μm)                                                                  0       0.895  0.796                                  45°                                                                           Marumerized (911 μm)                                                                        180     4.77   3.05                                   45°                                                                           Marumerized (911 μm)                                                                        165     3.98   2.55                                   30°                                                                           Marumerized (911 ρm)                                                                       165     2.00   1.77                                   30°                                                                           Marumerized (911 μm)                                                                        314     4.00   3.56                                   30°                                                                           Nalco (550 μm)                                                                              315     0.91   0.81                                   30°                                                                           Nalco (950 μm)                                                                              315     1.81   1.61                                   45°                                                                           Marumerized (911 μm)                                                                        620     10.0   6.4                                    45°                                                                           Marumerized (911 μm)                                                                        250     6.80   4.35                                   45°                                                                           Nalco (950 μm)                                                                              880     7.11   4.55                                   45°                                                                           Nalco (950 μm)                                                                              690     6.17   3.95                                   45°                                                                           Nalco (950 μm)                                                                              380     4.22   2.7                                    45°                                                                           Nalco (950 μm)                                                                              110     2.42   1.55                                   60°                                                                           Nalco (950 μm)                                                                              880     7.3    3.4                                    60°                                                                           Nalco (950 μm)                                                                              690     6.6    3.1                                    60°                                                                           Nalco (950 μm)                                                                              460     5.4    2.5                                    60°                                                                           Nalco (950 μ m)                                                                             230     3.3    1.6                                    60°                                                                           Nalco (950 μm)                                                                              0       1.8    0.85                                   60°                                                                           Cobalt (990 μm)                                                                             90      20.7   9.9                                    60°                                                                           Cobalt (990 μm)                                                                             40      10.1   4.7                                    60°                                                                           Cobalt (990 μm)                                                                             0       5.8    2.7                                    60°                                                                           Cobalt (347 μm)                                                                             90      7.5    3.5                                    60°                                                                           Cobalt (347 μm)                                                                             0       1.5    0.71                                   ______________________________________                                         .sup.1 Composite of 410 stainless steel particles of less than 40 μm       diameter encased in Nalco alumina at a concentration of 52 wt. % stainles     steel which were formed into beads of the indicated diameter by a rotatin     pan method.                                                                   .sup.2 Composite of 410 stainless steel particles in Catapul alumina          formed by mixing with ca. 60 wt. % 410 stainless steel particles of less      than 40 μm dia. and extruding the mix through a 0.025 inch diameter di     and then marumerizing the extrudates into bead form. (Marumerizer made by     Elanco Products Co., a division of Eli Lilly Co.)                        

EXAMPLE 3

This example demonstrates that the magnetically stabilized gascross-flow contactor is an excellent particulate capture device.

The contactor used in this experiment was identical to the contactorused in Example 2 having 45° angle louvers. The magnet modules used aredescribed below.

The magnet modules were comprised of 12 separate coils stacked on top ofone another at a spacing of about 6 cm. so that the bed could bevisually observed. The coils were 20.3 cm. internal diameter magneticmodules and occupied a height of 96.5 cm. The water cooled modules were4.13 cm. thick and 71.1 cm. outside diameter. Each module consisted of72 turns of square cross-section copper tubing which had a circular boreand which were capable of dissipating 60 KW with a cooling water flowrate of 6.8 liters per minute. The maximum center line field strengthobtained with the 12 modules connected in series was about 2200 oerstedsat an applied current of 250 amperes. To prevent the magnetic fieldstrength of the ends of the vertically arranged coils from decreasing inan undesirable manner as a function of axial distance, the modules ateither end were spaced 0.63 cm. apart while the spacing between theremaining 8 modules was 6.03 cm. The two modules at either end of thestack were connected in series to separate power supplies so theircurrent flow could be varied independently of the remaining 8 modules.The 8 centrally located modules were connected in series to a thirdpower supply.

The contactor was filled with cobalt particles having an average meandiameter of about 900 microns. Air containing 1.7 grains/SCF of nominalfly ash particulates was passed through the magnetically stabilizedcross-flow gas contactor containing the cobalt particles at asuperficial gas velocity of 94.5 cm./sec. at 0, 30 and 105 oersteds ofapplied magnetic field. The air containing the fly ash particulates wasfed to the contactor by use of a particulate feeder. The particulatefeeder utilized was a grooved rotary disc feeder (BIF, Providence, R.I.,the Omega model 22-01) which metered the particulates flow by varyingthe rotational speed of the disc. Very large changes in feed rate couldbe obtained by substituting a disc which had a larger groove. Therotational speed change of the disc was made possible by a 100:1 gearratio transmission. The particulates to be fed were dropped from a 0.028cubic meter hopper onto the rotating disc. A porous container of amoisture absorbant was hung inside the hopper, which was purged with drynitrogen. A plow, with a protrusion machined to the dimensions of thegroove, pushed the particulates off the edge of the disc. Theparticulates fell, under the influence of gravity, into a glass funnellocated under the outer edge of the disc. The funnel was attached to thesuction tap of a pneumatic syphon which was supplied with dry air.During the normal operation, a negative pressure, at the suction tap,entrained the particulate into the high velocity air jet which existedat the throat of the venturi inside the syphon. With this feedingarrangement the feed rate of particulates into the contactor wasindependent of the air flow rate through the syphon. The accumulation ofparticulates on the inner walls of the syphon and the interconnectingtube (0.95 cm. ID.) between the syphon discharge port and theparticulate-air injector was prevented by the high air velocity throughthe system. The average air velocity in the particulate transport linebetween the syphon and the particulate-air injector was 119 meters/sec.The air pressure to the syphon inlet could be varied up to 344 kPa.which resulted in an air flow rate of 509 liters/min.

The particulate feeder was calibrated with 0-50 micron fly ash which wassieved from a drum of fly ash obtained from a fluidized bed coalcombustor (FBCC).

The fly ash particulate feed rate could be varied from zero to 15.65gm./min. by varying the transmission speed of the feeder. The linearplot of transmission speed as a function of fly ash feed rate was foundto be reproducible within ±2% over the entire range of feed rates.

The outlet air and uncaptured particulates exited the outlet louvers tothe outlet plenum. An off-gas system was connected to the outlet plenumto a combination of Balston filters. Downstream from the Balston filtersthe cleaned air went into an exhaust duct which was vented to theatmosphere. The entire off-gas system was fabricated from 5 cm. ID,clear polyvinylchloride pipe so that any accumulation of particulates onthe walls of the pipe could be observed.

The modified Balston filters, which consisted of a fiberglass elementcontained in a transparent acrylic vessel were utilized to determine thegross particulate capture efficiency of the capture bed. The filterswere modified by reversing the flow through them; the flow path was fromthe inside of the filter element to the outside. The support core forthe element was removed and the element-end-seals were held in placewith two elastic bands. In this manner, none of the particulates everdeposited on the inner wall of the acrylic shell. When the particle sizedistribution, in the range of 1.1-7.0 microns, of the off-gas stream wasto be determined, the flow could be diverted by means of a two-way ballvalve, for a predetermined period, through modified Anderson impactors.The Anderson impactor contained four stages and a final filter havingeffective cut-off diameters ranging from greater than 7 microns to lessthan 1.1 microns in the final filter at 566 liters/min. flow rate.

The conventional Anderson impactor was modified slightly by the additionof a particle fractionator which limited the size of the particlesimpacting upon the first stage, to 11 microns. This was necessary inorder to prevent overloading of the first stage with large particulateswhich would be re-entrained and carried over to the second stage. Themaximum loading of any one stage of the Hi-Vol Anderson impactor was0.075 gm. ±10%. If this loading were exceeded, the particle size cut offdata would be questionable.

The particle fractionator which was incorporated into the impactor wasdesigned from published data (Willeke, K. and McFeters, J., "Calibrationof the Champ Fractionator," (Final Report) Particle Tech. Lab. Dept. ofMech. Eng., Minneapolis, Minn. 55455, March, 1975, Publication No. 252).

The preweighed Balston filter elements were removed and their weightchange measured on a precision balance that had a sensitivity of 0.001gm. Fly ash that had accumulated on the walls of the off-gas system wascollected and weighed. The bed material, which now contained the fly ashcaptured after each experiment, was removed from the reactor andweighed. After weighing the bed it was necessary to separate the 0-50micron fly ash from the 900 micron cobalt particles. This wasaccomplished via mechanical sieving in a vibrating sifter. The flyash-cobalt mixture was screened through a sieve for a short period. Uponinspection of the sieve material under a microscope it was determinedthat all the fly ash had been removed from the cobalt. The fractions offly ash and cobalt were weighed, a mass balance and bed captureefficiency computed.

The capture efficiency for the bed of each experiment was determined bycomparing the total weight of fly ash actually fed to the contactor (aweight measurement) as determined from an ash feeder calibration curve,less the ash found in the inlet plenum, to the sum of the fly ashcollected in the Balston filters and accumulated in the off-gas linesupstream of the filters. The fly ash material balance was calculatedfrom the ratio of total fly ash fed to the contactor (obtained from acalibration curve) to the total fly ash accumulated in the bed (the flyash was removed from the cobalt bed solids by a vibrating screen device,e.g., a Sonic Sifter), the off-gas piping and the Balston filters.

The capture efficiency was calculated by two methods: ##EQU3##

In general, both methods gave similar results indicating a completeaccounting for all particulates fed to the contactor.

The results of these static bed particulate capture tests are shown inFIG. 12 wherein the capture efficiency data is plotted against time(minutes). As shown in FIG. 12 the capture efficiency drops off veryrapidly at 0 applied magnetic field. An improvement in captureefficiency occurs at 30 oersteds of applied magnetic field and adramatic improvement in capture efficiency occurs at 105 oerstedsapplied magnetic field. Thus, the applied magnetic field not onlyenables one to use higher gas velocities before blowout, as shown inExamples 1 and 2, it also improves the capture efficiency of a gas crossflow contactor.

EXAMPLE 4

This example demonstrates that the magnetically stabilized gascross-flow contactor can be used in a continuous manner as a particulatecapture device.

The contactor and magnet modules used in this experiment were identicalto the contactor used in Example 3. The contactor, however, was modifiedto the extent that it had a valve means above and below the contactor tocontrol the solids input and output. The magnetizable solids (cobalt,having a mean diameter of 590 microns) were added to a solids hopperabove the contactor. The contactor was filled by opening the inlet valveand closing the solids outlet valve. In operation, the solids exit thecontactor through a vertical standpipe upon opening the solids openingvalve whereupon the solids are transported to a solids elutriator toseparate the fly ash from the solids and then pneumatically transportedup a pipe to a cyclone and down into the solids hopper. In this mannerthe solids can be moved throughout the entire system in a controlled andcontinuous manner.

The tests in this example, other than the solids circulation, wereconducted in a manner similar to that described in Example 3. Dried aircontaining fly ash was fed to the contactor by use of the rotating disccalibrated feeder. The outlet gas was fed to an "Octopus" Balston filtermanifold. Table II summarizes five (5) runs using the circulating bed at120 and 100 oersteds of applied magnetic field. As shown from the datain Table II, the following advantages are manifested by use of thesolids circulating magnetically stabilized gas cross-flow bed:

Low pressure drops were maintained across the reactor throughout all theruns, i.e., pressure drops remained below 3 inches of water/inch of bedfor all runs;

Increasing the fly ash (F/A) level in the inlet gas did not reducecapture efficiency;

Increasing the solids circulation rate did not reduce captureefficiency;

The data in Table III show that the instantaneous and cumulative captureefficiencies for all runs tested were greater than 99%. These highcapture efficiencies were obtained even after an average of 17theoretical cycles of the capture solids (calculated on the rate ofsolids movement). This evidence suggests that fly ash can be effectivelyremoved from the bed material to prevent a subsequent reduction incapture efficiency because of fly ash reentrainment in the granularcapture bed; and

Fractional capture efficiencies, as obtained using an Anderson impactor,were high for all particulates greater than 1 micron. Table IV shows thefractional efficiencies of particulates for various size ranges.

                                      TABLE II                                    __________________________________________________________________________    CIRCULATING BED RUN SUMMARIES                                                 using ˜ 580 MICRON D.sub.p COBALT AS CAPTURE MEDIA                      <44 MICRON FBCC FLY ASH.sup.(5)                                                                                            Range of                                                                      ΔP                                                                           EOR.sup.(3)                                                                          EOR                  Circulating                                                                         Gas   Fly Ash                                                                              Bed  Applied                                                                            Run             Across                                                                             Cumulative                                                                           Theoretical          Bed   Velocity,                                                                           Loading,                                                                             Velocity,                                                                          Field,                                                                             Length,                                                                            MB.sub.A,.sup.(1)                                                                  MB.sub.B,.sup.(2)                                                                   Bed, Efficiencies,                                                                        Number of            Run   Ft./Sec.                                                                            Grains/SCF                                                                           In./Min.                                                                           Oe   Min. %    %     cm H.sub.2 O                                                                       %      Cycles               __________________________________________________________________________    1     2.92  1.42   1.33 120  138  92.17                                                                              99.71                                                                              11.5-17.5                                                                           99.60  2.9                  2     2.92  5.34   0.96 100  147  108.27                                                                             100.43                                                                             13.7-29.6                                                                           99.84  2.4                  3     2.95  1.78   4.88 100  200  83.51                                                                              99.97                                                                              12.6-24.0                                                                           99.77  16.7                 4     2.82  5.60   4.66 100  210  94.38                                                                              99.58                                                                              18.1-21.1                                                                           99.95  16.9                 5     2.82  6.22   4.39 100  645  87.65                                                                              99.61                                                                              12.7-26.1                                                                           (4)    49.1                 __________________________________________________________________________     .sup.(1) MB.sub.A = material balance on the fly ash.                          .sup.(2) MB.sub.B = material balance on the cobalt.                           .sup.(3) EOR = End of Run.                                                    .sup.(4) EOR cumulative efficiency is not reported for CB5 due to the         filling of the outlet louvers with bed solids over the course of the run.     .sup.(5) FBCC = Fluid Bed Coal Combustion.                               

                  TABLE III                                                       ______________________________________                                        CIRCULATING BED FILTERS                                                       DEMONSTRATE EXCELLENT                                                         PARTICULATE REMOVAL AFTER SEVERAL CYCLES                                      Circ-                                                                         ulating           Theoretical                                                                              Efficiencies                                     Bed     Time of   Number of  Instantaneous,                                                                        Cumulative                               Run     Run, Min. Solid Cycles                                                                             %       %                                        ______________________________________                                        1       25        0.52       99.19   99.19                                            50        1.05       99.73   99.46                                            70        1.47       99.73   99.54                                            105       2.20       99.70   99.59                                            138       2.89       99.65   99.60                                    2       30        0.49       99.72   99.72                                            60        0.98       99.80   99.76                                            90        1.48       99.97   99.83                                            120       1.97       99.94   99.86                                            147       2.41       99.78   99.84                                    3       30        2.50       99.53   99.53                                            60        5.00       99.77   99.65                                            90        7.51       99.81   99.70                                            120       10.01      99.80   99.73                                            150       12.51      99.80   99.74                                            180       15.01      99.85   99.76                                            200       16.68      99.89   99.77                                    4       30        2.41       99.95   99.95                                            60        4.82       99.99   99.97                                            90        7.22       99.92   99.96                                            120       9.63       99.93   99.95                                            126       10.11      99.46.sup.1                                                                           99.93                                            150       12.04      99.97   99.93                                            180       14.44      100.00  99.95                                            210       16.85      99.99   99.95                                    5.sup.2 30        2.28       99.76                                                    90        6.85       99.87                                                    102       7.76       99.74.sup.3                                              162       12.32      99.88                                                    222       16.89      99.83                                                    237       18.03      99.71.sup.3                                              282       21.45      99.79                                                    342       26.01      99.94                                                    402       30.58      99.98                                                    462       35.14      99.98                                                    565       42.98      99.95                                                    582       44.27      99.86                                                    597       45.41      99.99.sup.3,4                                            627       47.69      99.94                                                    645       49.07      99.93                                            ______________________________________                                         .sup.1 Represents Anderson impactor data.                                     .sup.2 Only instantaneous efficiencies are quoted because the outlet          louver chamber gradually filled during the run.                               .sup.3 Anderson impactor data.                                                .sup.4 Tare weights of filter paper greater than gross weights in all but     one case.                                                                

                  TABLE IV                                                        ______________________________________                                        FRACTIONAL CAPTURE EFFICIENCIES OF                                            MAGNETICALLY STABILIZED GAS CROSS-FLOW BED.sup.1                                               Fractional Efficiencies                                      Size Range,      During Theoretical Cycles                                    Microns          16.89 to 18.03 (in wt. %).sup.2                              ______________________________________                                        >7.0             99.74                                                        3.3-7.0          99.90                                                        2.0-3.3          99.63                                                        1.1-2.0          97.79                                                        <1.1             92.49                                                        ______________________________________                                         .sup.1 Conditions: Run 5, Tables II and III.                                  .sup.2 Theoretical cycle numbers were calculated based on contactor           volume, the solids volumetric circulation rate, and the elapsed time afte     start of run.                                                            

EXAMPLE 5

Tests were carried out to determine the effects of particle size oncopper utilization in a simulated flue gas desulfurization process.

One sorbent, sorbent A, was a conventional sized copper surfaceimpregnated porous alumina prepared as described in U.S. Pat. No.3,985,682. More particularly, sorbent A was prepared as follows: 1/2inch O.D. cylindrical ring extrudates (having, 1/4 inch holes) of aceticacid peptized porous alumina previously calcined for 3 hours at 1000° F.(B.E.T. surface area, about 180 m² /g; a pore volume of about 0.40 cc/g)were immersed in a mixture of isomeric C₆ alcohols (oxo alcohols) for 1hour. The alcohol which was used to minimize penetration of the coppercontaining solution during copper impregnation. The extrudates wereremoved from the alcohol solution, drained of excess alcohol and werethen immersed in a solution of Cu(NO₃)₂.3H₂ O and MgNO₃ to provideapproximately 5 wt. % Cu and 0.3 wt. % Mg on Al₂ O₃ in the regionactually impregnated by the CuNO₃ and MgNO₃ solution. The extrudateswere permitted to remain in the solution until the alcohol was displacedto a depth of 0.035 inches by the Cu as described in U.S. Pat. No.3,985,682. The extrudates were then removed from the copper nitratesolution, drained, blotted dry and dried in a forced air drying ovenovernight at about 195° F. The nitrates were decomposed to oxides bycalcining under air at 800° F. for about 3 hours.

Sorbents B-1, B-2 and B-3 were prepared in the same manner as Sorbent A(the alumina had a B.E.T. surface area of 247 m² /g; pore volume of 0.54cc/g.) except that the alcohol immersion step was omitted since totalcopper impregnation was desired with the smaller particles. The copperimpregnated extrudates were crushed and screened to three differentsizes, 80/100 mesh (average particle size 160 microns), 42/60 mesh(average particle size 330 microns) and 10/20 mesh (average particlesize 1400 microns) for Sorbents B-1, B-2 and B-3 respectively. Thesorbent particles were then tumbled for 1/2 hour to remove the roughedges and then rescreened. The final Cu analysis for each of the threesizes of particles was 4.54 wt. %, 4.78 wt. % and 4.90 wt. %, forSorbents B-1, B-2 and B-3, respectively, for Cu and Mg the analysis wasabout 0.3 wt. % for each of the three particle sorbent sizes.

The testing unit consisted of a sandbath-heated, 16 mm quartz reactor ofdownflow design. The gas feed blend (measured by rotameters) plus waterwas introduced at the inlet tube and passes down to near the bottom ofthe reactor, up through a preheating coil and entered the reactor abovethe sorbent. The gas flow continued downward through the sorbent bed andout the gas exit line through a knockout pot to an SO₂ analyzer (airpollution monitor manufactured by Dyansciences Corp. equipped with a55-330 sensor). Provision was made for by-passing the reactor so as topermit analysis of the feed gas.

The simulated flue gas had the following approximate volume percentcomposition:

    ______________________________________                                        Component          Volume Percent                                             ______________________________________                                        CO.sub.2           10.2                                                       O.sub.2            2.1                                                        SO.sub.2           0.27                                                       H.sub.2 O          10                                                         N.sub.2            Balance                                                    ______________________________________                                    

The simulated processes were carried out by placing about 20 cc volumeof the test sorbent in the reactor placed in the sandbath and brought toa temperature of 700° F. The SO₂ analyzer was checked against acertified Matheson SO₂ gas blend as standard. Using the reactor by-passthe feed gas blend was checked for proper SO₂ content and the gas rate(3 liters/1 minute) was checked using a wet test meter. Water was fed bya Ruska pump and vaporized in the reactor inlet preheater. The sorptionwas carried out at atmospheric pressure. Prior to starting the sorptioncycle the reactor was lined out with all gases and water except SO₂passing over the sorbent. At the start of the sorption cycle SO₂ was cutin and the amount of SO₂ in the exit gas measured as a function of timeusing the SO₂ analyzer. When the SO₂ content in the exit gas reached1000-1100 ppm the sorption cycle was terminated by cutting off all thegases except nitrogen. The reactor was purged with nitrogen-steam(85/15) for 4 minutes at the rate of approximately 2 l./min. Thenitrogen was then cut out, and the sorbent regenerated by cutting in H₂-steam (50/50 mixture ca. 600 cc/min.) for 20 minutes. At the end of theregeneration cycle the sorbent was purged again with nitrogen for 4minutes. Then all of the gases (except SO₂) were passed over the sorbentand through the analyzer until the analyzer was showing zero SO₂.Another sorption cycle was then initiated by cutting in the SO₂. Thepercent sulfation (copper utilization) was calculated from the exit SO₂concentration-time data when 300 ppm SO₂ in the exit gas was scorded.Copper utilization was also calculated at the 90% cumulative SO₂ removallevel. The following table illustrates the affect of particle size inthe fixed bed simulated flue gas desulfurization process.

                  TABLE V                                                         ______________________________________                                        COMPARISON OF SMALL PARTICLE                                                  SIZE SORBENT U.S. 1/2" RINGS                                                  IN SIMULATED FLUE GAS                                                         DESULFURIZATION                                                                                Copper on Magnesia                                                            Stabilized Al.sub.2 O.sub.3                                  Sorbent            Sorbent A  Sorbent B-1                                     ______________________________________                                        Size               1/2 inch rings                                                                           80/100 Tyler                                                                    mesh                                          Temperature        730° F.                                                                           700° F.                                  Gas Space Velocity.sup.(1)                                                    V/Hr/V             2500       8800                                            V/Hr/W             7.5        20.7                                            Approximate Copper Utilization                                                at 300 ppm                                                                    SO.sub.2 Breakthrough                                                                            30-38%     70%                                             Approximate Copper Utilization                                                at 90%                                                                        SO.sub.2 removal   45-50%     95%                                             ______________________________________                                         .sup.(1) The feed rate per gram of copper was similar in the two cases.  

The data Table V show that at over 3 times the V/Hr/V space velocity thesmaller sorbent has substantially more copper utilization as the 1/2inch rings. Thus one would expect that by using the smaller sorbentsized higher through-puts and improved copper utilizations would bepossible.

Further tests were conducted with the same simulated flue gas at a spacevelocity of 8800 V/Hr/V and at 700° F. using Sorbents B-1, B-2 and B-3to establish a direct comparison on the effect of particle size. Thefollowing table (Table VI) summarizes the results of these tests.

                  TABLE VI                                                        ______________________________________                                        Effect of Particle Size on Copper Utilization.sup.(1)                                Sorbent                                                                       Mesh     Avg.                Wt. % Cu.sup.(2)                          Sorbent                                                                              Size     Particle Size                                                                             Wt. % Cu                                                                              Utilized                                  ______________________________________                                        B-1     80-100  160         4.54    70                                        B-2    42-60    330         4.78    58                                        B-3    10-20    1400        4.90    50                                        ______________________________________                                         .sup.(1) Feed gas vol. % 10.2%, Co.sub.2 ; 2.1%, O.sub.2 ; 0.27% SO.sub.2     ; 10% H.sub.2 O; Balance N.sub.2. Conditions: V/Hr/V ca. 8800; Temperatur     700° F., Pressure ca. atmospheric                                      .sup.(2) As measured when 300 ppm SO.sub.2 is reached in the exit gas.   

The above data clearly show an advantage in copper utilization for useof the smaller particle size sorbents. Further tests at 650° F. and 750°F. show that this advantage exists at these temperatures as well. Infact increasing the temperature from 650° F. to 750° F. showed anincrease in sulfation (copper utilization) as shown in Table VII.

                  TABLE VII                                                       ______________________________________                                        Effectt of Temperature on Copper Utilization.sup.(1)                                                       Cum. %                                           Temperature, °F.                                                                   Wt. % Cu Utilized.sup.(2)                                                                      SO.sub.2 Removed                                 ______________________________________                                        650         43               98                                               700         70               98                                               750         89               99                                               ______________________________________                                         .sup.(1) Sorbent B1, Feed gas vol. % 10.2% CO.sub.2 ; 2.1% O.sub.2 ; 0.27     SO.sub.2 ; 10.0 H.sub.2 O, basance N.sub.2. Conditions: V/Hr/V ca. 8800,      Temperature 700° F., Pressure ca. atmospheric;                         .sup.(2) As measured when 300 ppm SO.sub.2 is reached.                   

Since it is necessary to use sorbent having magnetic properties in theprocess of the invention tests were conducted using compositemagnetizable sorbent particles. The preparation of a SO₂ sorbent for usein the magnetic bed entailed the coating of stainless steel (410 SS)with alumina followed by impregnation of this "magnetic alumina" withcopper and magnesium. Comparing sorbents prepared with this "magneticalumina" vs. a spray dried alumina, provided information on the effectsof stainless steel on copper utilization. Also, comparing the magneticproperties of fresh vs. discharged sorbent, data was obtained whichdetermines whether operations in a flue gas environment affects themagnetic properties of the sorbent. Table VIII illustrates the resultsof tests showing the copper utilization of magnetic and non-magneticsorbents.

                  TABLE VIII                                                      ______________________________________                                        Copper Utilization of Magnetic Sorbents.sup.(1)                               Sorbent      C-1.sup.(2)                                                                            C-2.sup.(3)                                                                            C-3.sup.(4)                                                                          C-4.sup.(5)                             ______________________________________                                        Cu, Wt. % on                                                                  Sorbent.sup. (6)                                                                           4.71     2.74     4.03   2.74                                    Cu, Wt. % on                                                                  Al.sub.2 O.sub.3                                                                           5        5        7.5    5                                       Cu Utilization                                                                at 300 ppm                                                                    SO.sub.2 break-                                                               through      46       38       46     39                                      ______________________________________                                         .sup.(1) Feed gas vol. % 10.2% CO.sub.2 ; 2.1% O.sub.2 ; 0.27% SO.sub.2 ;     10% H.sub.2 O, balance N.sub.2. Conditions: V/Hr/V 8500; 50/100 mesh          partcles; 700° F.                                                      .sup.(2) Sorbent C1 is a copper on spray dried Al.sub.2 O.sub.3 having a      B.E.T. surface area of 285 m.sup.2 /g and a pore volume of 1.15 cc/g. The     spray dried alumina which had been calcined for 2 hours at 1000° F     was impregnated with Cu(NO.sub.3).sub.2  . 3H.sub.2 O and                     Mg(NO.sub.3).sub.2  . 6H.sub.2 O dissolved in acetone to give                 approximately 5% Cu and 0.3% Mg on the alumina. The sorbent was air dried     and calcined for 3 hours at 800° F. and rescreened at 50/100 mesh.     Cu analysis = 4.04% (theor. 4.71%) and Mg analysis 0.28%.                     .sup.(3) Sorbent C2 is a copper on Al.sub.2 O.sub.3 containing stainless      steel prepared as follows: 30 gms. of "magnetic Al.sub.2 O.sub.3 " (410       stainless steel coated with Al.sub.2 O.sub.3 43/57) of 50/100 mesh were       impregnated with copper nitrate and magnesium nitrite to give a nominal 5     wt. % Cu and 0.3 Mg on Al.sub.2 O.sub.3 using acetone as the solvent. The     sorbent was air dried, calcined for 3 hours at 800° F. and             rescreened to 50/100 mesh. The Cu analysis was 2.92% (theor. 2.74%) and M     (theor.) was 0.16%.                                                           .sup.(4) Sorbent C3 is a copper on Al.sub.2 O.sub.3 containing stainless      steel prepared as follows: 30 gms of the "magnetic Al.sub.2 O.sub.3 "         described above for C2 were impregnated as in C2 to give 7.5% Cu and 0.3%     Mg on Al.sub.2 O.sub.3 basis, % Cu (analysis) on sorbent was 4.13 (theor.     4.03%.                                                                        .sup.(5) Sorbent C4 is a physical mixture (43/57) of 410 stainless steel      particles and sorbent C1 (4.71% Cu on spray dried Al.sub.2 O.sub.3) was       prepared. This mixture gave a theoretical copper content in the mixture o     2.74%. (This run was conducted at a space velocity of 6600 V/Hr/V ca.         .sup.(6) Calculated values are reported in the Table.                    

The data in Table VIII show that Sorbent C-2 had a lower activity thanthe spray dried alumina (possibly due to copper interaction with thestainless steel during the copper impregnation step) but the activitywas restored to that of the spray dried alumina sorbent C-1 when thelevel of Cu was increased to a nominal 7.5%. The physically mixed,magnetic sorbent C-4 possessed equivalent activity to the impregnatedmagnetic sorbent at 700° F. albeit at a somewhat lower space velocity.At 750° C., compare C-2 vs C-4, the activity for the physically mixedsorbent was somewhat lower (53% vs. 61%). The fact that the sorbentprepared by physical mixing the stainless steel with copper on aluminasorbent showed lower activity than the sorbent prepared by impregnatingcopper on alumina-coated stainless steel, would seem to rule out anyharmful interaction with the stainless steel during theimpregnation-calcination step used to prepare the latter sorbent.

The magnetic properties of the discharged sorbents were tested and thedata obtained indicated that the magnetic properties of the dischargedsorbent did not change markedly relative to those of the fresh sorbent.These results indicate that the stainless steel is not beingsignificantly oxidized or reduced under the test conditions.

The sorption of SO₂ using the simulated flue gas feed on various 10/20mesh metal oxides (e.g. ThO₂, U₃ O₈, Al₂ O₃ and MalO₄ (M=a metal) andZrO₂ coated alumina) at low temperatures (e.g., 250°-300° F., and at aspace velocity of 6,000 V/Hr/V) followed by nitrogen-steam regenerationat 750° F. (space velocity: 3,000 V/Hr/V) showed that the zinc aluminaspinel (ZnAlO₄) to be the most active followed by a zirconia coatedalumina and alumina. Sorption cycles were remarkably consistent asmeasured by the time required to achieve 300 ppm SO₂ in the exit gas.

Lime (calcium oxide) is also a feasible SO₂ sorbent in anon-regenerative process. The lime sorbent useful in the practice in thepresent invention is a physical mixture of a fluidizable magneticsubstance (e.g., stainless steel, cobalt, cobalt alloys, etc.) and lime.The sulfated or sulfited lime after separation is not regenerated. Whenusing lime as a sorbent it is advisable to use relatively highertemperatures, e.g., 900° F. and higher, particularly for smallerparticle sizes, e.g., 20-60 mesh lime particles. At the highertemperatures, however, care should be directed to selection of themagnetic particles so that the curie point of the magnetic particles isnot encountered at the operating temperatures.

In addition to the sorbents described above, other flue gasdesulfurization sorbents may be utilized in the magnetically stabilizedcross-flow contactor. For example, the cerium oxide sorbent disclosed inU.S. Pat. No. 4,001,375, the disclosure of which is incorporated hereinby reference, may be used as a composite or in admixture with suitablemagnetic particles. In such a process the flue gas may be contacted withthe cerium oxide-magnetic composite or admixture at a temperatureranging from 300° C. to 800° C. to form cerium sulfate and/or sulfiteand regeneration of the sorbent can be accomplished by contacting thesorbent with a reducing gas, for example, hydrogen is admixture withsteam or other inert gases at a temprature ranging from 500° C. to 800°C. to convert the cerium sulfate or sulfite to cerium oxide. During theregeneration step, the desorbed species is initially sulfur dioxide.However, when about 50% of the sulfur is removed from the sorbent, thedesorbed species becomes H₂ S. Thus, an admixture of SO₂ and H₂ S areprovided with the excess reducing gas, which can be fed conveniently tothe Claus plant for conversion into elemental sulfur. Preferably, thecerium oxide will be on an inert support. The unsupported cerium oxidewill preferably have a B.E.T. surface area of at least 10 m² /g., morepreferably 20-40 m² /g.

Another example of sorbents useful in the flue gas desulfurization inthe magnetically stabilized cross-flow contactor comprises magneticcomposites or admixtures of the sorbents disclosed in U.S. Pat. No.4,001,376, the disclosure of which is incorporated herein by reference.Such sulfur dioxide sorbents are comprising of a porous gamma-aluminabase, about 2-20 wt. % (based on alumina) of a coating of a refractoryoxide such as titanium dioxide, zirconium dioxide, or silica, and anactive material, such as copper oxide, which is capable of selectiveremoval of sulfur oxides from a gas mixture.

EXAMPLE 6

A simulated flue gas desulfurization process utilizing the magneticallystabilized cross-flow contactor was designed based, in part, on thefixed bed data in Example 5. The design basis consisted of treating aflue gas from a coal-fired boiler generating approximately 2 M lbs/hr ofsteam. The coal is Illinois No. 6, but with the ash level increased tomatch the flue gas from East Texas Lignite. This gives both the highestSO₂ and fly ash loadings. Coal and flue gas compositions and conditionsare given below. The flue gas temperature is between 700°-750° F. Thistemperature corresponds roughly to the temperature into the boiler airpreheater.

The design basis for SO_(x), NO_(x), and particulate removal is asfollows:

    ______________________________________                                        NO.sub.x          0.15 lb/M Btu                                               SO.sub.x          0.3 lb/M Btu                                                Particulates      0.02 lb/M Btu                                               ______________________________________                                    

The specific design basis for each process step (identified hereafter bystream numbers) are given in Table IX.

The magnetically stabilized cross-flow flue gas cleanup system is a drysorbent process that simultaneously removes SO_(x), NO_(x), andparticulates from flue gas. The system consists of a multipanel bedcontactor (as shown in FIG. 6) where the SO_(x), NO_(x), andparticulates are removed, an elutriator where particulates are strippedfrom the circulating catalyst and collected for disposal, and aregenerator where the sorbent is regenerated and SO₂ liberated fordownstream recovery. The sorbent consists of 30 wt.% alumina spheres(impregnated with 5 wt.% copper) and 70 wt.% 410 stainless steelparticles (which give the sorbent magnetic properties) having a particledensity of 137 lb/ft³ (2.2 g/cm³) and a bulk density of 75.5 lb/ft³. Theparticle size ranged from 250-1680 mm.

Flue gas (stream 1) is taken from a boiler economizer section at700°-750° F. and mixed (stream 3) with NH₃ (stream 2) before entering(stream 4) the magnetically stabilized cross-flow contactor. The ammoniaacts to decompose the NO_(x) via the following overall reaction:##STR1##

In the reactor the flue gas flows cross-current at a superficial gasvelocity through the panel area of 3 ft/sec (5 ft/sec through thelouvers) to a magnetically stabilized moving bed or sorbent, which istraveling vertically down the reactor panels having a thickness of 9inches. The temperature in the bed is about 748° F. The pressure drop inthe bed is 15 inches of water (bed and louvers) and the maximum spacevelocity is 6500 V/V/H. The maximum catalyst dust loading is 3 wt.% andthe maximum copper sulfation is 75%. The applied magnetic field is heldat 300 oersteds by use of 5 magnet modules to provide a substantiallyuniform applied magnetic field over the entire length of the bed. Herethe particulates are trapped by the sorbent spheres the NO_(x)decomposition is catalyzed, and SO₂ is adsorbed according to thereaction:

    SO.sub.x +Cu+O.sub.2 →CuSO.sub.4

Clean flue gas (stream 5) passes out of the reactor and on to the boilerair preheater, induced draft fan, and stack. The decomposition andadsorption reactions are both exothermic and the exiting flue gas leavesat 750°-800° F.

The magnetic sorbent from the reactor (stream 6) flows by gravity to theelutriator through magnetic lock hoppers on each panel which regulatethe sorbent circulation rate and ensure even flow through the panels. Inthe elutriator, (having a bed temperature of 711° F. and a pressure ofabout 3 psig) fly ash collected in the reactor is elutriated from thesorbent with air at 2-3 ft/sec. (stream 7) and collected in cyclones viastream 8 for disposal. The temperature in the cyclones is about 710° F.Overhead (stream 17) from the cyclones recycles to the top of thereactor sorbent distributor. The fly ash is drawn off of the cyclonesvia stream 16.

From the elutriator, sorbent is transferred to the regenerator throughan overflow line (stream 9). The fluid bed in the regenerator (having abed temperature of 719° F. and a pressure of 10 psig.) is magneticallystabilized by the action of an electromagnetic coaxially surrounding theregenerator vessel, and the spent sorbent flows downward through theregenerator bed, countercurrent to the regenerator gas (stream 10). Theapplied magnetic field on the regenerator vessel is 200 oersteds toprovide a voidage of 0.6. The sorbent is regenerated by the followingoverall reaction:

ti CuSO₄ +2H₂ →Cu+2H₂ O+SO₂

SO₂ from the regenerator passes overhead (stream 11) to downstreamrecovery in a Claus plant or sulfuric acid plant. The regeneratedsorbent is transferred back (stream 12) to the reactor via a riser usingaeration air (stream 13) and distributed to the panels via a transferline (stream 14) by a small fluid bed above the panels. The solids andair from stream 13 are separated and the air is emitted via a transferline (stream 15) where this line is joined with the sorbent distributoroverhead (stream 18).

Table IX below shows the design basis for the individual pieces ofequipment in the flue gas desulfurization process described above inthis example.

                                      TABLE IX                                    __________________________________________________________________________    HEAT AND MATERIAL BALANCE                                                     MSB FLUE GAS CLEANUP PROCESS                                                  Stream Number                                                                             1           2      3        4      5     6                        Stream      Flue Gas From                                                                             Amonia Recycle  Reactor                                                                              Clean Flue                                                                          Spent                    Name        Boiler      Injection                                                                            Air      Feed   Gas   Sorbent                  __________________________________________________________________________    Temperature, °F.                                                                   700         60     737      710    748   748                      Pressure, psia          150                                                   (in. H.sub.2 O)                                                                           (-4.0)                             (-19.0)                        Gas Rate                                                                      Total kLb/Hr                                                                              2861.9      0.6    237.9    3099.8 3077.0                                                                              --                       Component MPH                                                                 CO.sub.2    12799.6     --     --       12799.6                                                                              12799.6                                                                             --                       H.sub.2 O   8018.4      --     170.2    8188.6 8244.5                                                                              --                       N.sub.2     71813.4     --     6578.1   78391.5                                                                              78431.3                                                                             --                       O.sub.2     3811.4      --     1560.6   5732.0 5222.6                                                                              --                       NO          56.0        --     --       56.0   14.0  --                       SO.sub.2    297.9       --     --       297.9  13.1  --                       H.sub.2     --          --     --       --     --    --                       CO          --          --     --       --     --    --                       CH.sub.4    --          --     --       --     --    --                       NH.sub.3    --          37.3   37.3     37.3   --    --                       Total MPH   96796.9     37.3   8346.2   105142.9                                                                             104725.1                                                                            --                       Sorbent Rate, kLb/Hr                                                          Al.sub.2 O.sub.3 + SS 410                                                                 --          --     --       --     --    4149.9                   Cu          --          --     --       --     --    0.0                      CuO         --          --     --       --     --    7.6                      CuSO.sub.4  --          --     --       --     --    45.5                     Anh         106.5       --     --       118.3  0.1   124.4                    Total       106.5       --     --       118.3  0.1   4327.4                   __________________________________________________________________________    Stream Number                                                                             7           8      9        10     11    12                       Stream      Elutriator  Elutriator                                                                           Deashed Spent                                                                          Regeneration                                                                         SO.sub.2                                                                            Regenerated              Name        Air         Overhead                                                                             Sorbent  Gas    Recovery                                                                            Sorbent                  __________________________________________________________________________    Temperature, °F.                                                                   95          711    711      750    719   917                      Pressure, psia                                                                (in. H.sub.2 O)                                                                           7           18.0            90     24.7                           Gas Rate                                                                      Total kLb/Hr                                                                              205.5       205.5  --       18.2   47.1  --                       Component MPH                                                                 CO.sub.2    --          --     --       180.3  180.3 --                       H.sub.2 O   143.7       143.7  --       450.6  1115.2                                                                              --                       N.sub.2     5555.3      5555.3 --       --     --    --                       O.sub.2     1478.3      1478.3 --       --     --    --                       NO          --          --     --       --     --    --                       SO.sub.2    --          --     --       --     284.8 --                       H.sub.2     --          --     --       664.9  0.0   --                       CO          --          --     --       26.1   26.1  --                       CH.sub.4    --          --     --       2.9    2.9   --                       NH.sub.3    --          --     --       --     --    --                       Total MPH   7177.3      7177.3 --       1324.8 1609.3                                                                              --                       Sorbent Rate, kLb/Hr                                                          Al.sub.2 O.sub.3 + SS 410                                                                 --          --     4149.9   --     --    4149.9                   Cu          --          --     0.0      --     --    24.1                     CuO         --          --     7.6      --     --    --                       CuSO.sub.4  --          --     45.5     --     --    --                       Anh         --          118.2  6.2      --     --    6.2                      Total       --          118.2  4209.2   --     --    4108.2                   __________________________________________________________________________    Stream Number                                                                             13          14     15       16     17    18                                                                      Elutriator                     Stream      Aeration Air to                                                                           Sorbent                                                                              Transfer        Cyclone                                                                             Sorbent Distributor      Name        Regen Sorbent Riser                                                                       to Reactor                                                                           Line Air Fly Ash                                                                              Overhead                                                                            Overhead                 __________________________________________________________________________    Temperature, °F.                                                                   95          743    743      710    710   741                      Pressure, psia                                                                            75                                                                (in. H.sub.2 O)                                                               Gas Rate                                                                      Total kLb/Hr                                                                              37.8        --     31.8     --     205.5 205.5                    Component MPH                                                                 CO.sub.2    --          --     --       --     --    --                       H.sub.2 O   26.5        --     26.5     --     143.7 143.7                    N.sub.2     1022.8      --     1022.8   --     5555.3                                                                              5555.5                   O.sub.2     272.2       --     82.3     --     1478.3                                                                              1478.3                   NO          --          --     --       --     --    --                       SO.sub.2    --          --     --       --     --    --                       H.sub.2     --          --     --       --     --    --                       CO          --          --     --       --     --    --                       CH.sub.4    --          --     --       --     --    --                       NH.sub.3    --          --     --       --     --    --                       Total MPH   1321.5      --     1131.6   --     7177.3                                                                              7177.3                   Sorbent Rate, kLb/Hr                                                          Al.sub.2 O.sub.3 + SS 410                                                                 --          4149.9 --       --     --    --                       Cu          --          0.0    --       --     --    --                       CuO         --          30.2   --       --     --    --                       CuSO.sub.4  --          --     --       --     --    --                       Anh         --          6.2    --       106.4  11.8  11.8                     Total       --          4186.3 --       106.4  11.8  11.8                     __________________________________________________________________________

The above examples show the usefulness of the magnetically stabilizedgas cross-flow contactor as a particulate capture device at utilityboiler pressures and temperatures. The contactor may also be used toremove particulates and other contaminants at high temperatures andpressures. For example, the magnetically stabilized gas cross-flowcontactor may be used to remove particulates and chemical contaminatesfrom flue gas streams from a pressurized fluidized bed combustor (PFBC)at temperatures ranging from 1500°-1700° F. and pressures ranging from5-20 atmospheres. At such high temperatures and pressures, particularlyunder the oxidative and corrosive conditions due to the flue gas, it isdesirable to use the cobalt-containing particles described in copendingU.S. application Ser. No. 384, the disclosure of which is incorporatedherein by reference. This high temperature and pressure capture,collection and chemical scavenger process may be practiced by use of themagnetically stabilized gas cross-flow contactor described herein. Forexample, the devices shown in FIGS. 4-10 may be used.

In typical pressurized fluidized bed combustion applications, flue gascontains 4-10 grs/SCF exiting from the combustor with a particle sizedistribution ranging from 1-600 microns. It is generally desirable tohave a hot gas cleanup system having an overall collection efficiency of99.9%. Additionally, graded efficiencies of 99.95% for particulatesgreater than 5 microns, 99.5% for particulates between 4-5 microns, and99.5% for particulates less than 4 microns should be removed. One way toaccomplish the above particulate capture standard in a combined cyclepower generation system under high temperatures and pressures is toslightly modify the schematic shown in FIG. 8 by incorporating cyclonesin series between the fluid bed combustor and the magneticallystabilized cross-flow contactor. The purpose of the cyclones is toprovide efficient and economical removal of particulates greater than 4microns, thereby reducing the amount of material which must be removedby the magnetically stabilized cross-flow contactor. This will have afavorable impact in reducing the capital and operating costs since itwill reduce the size and complexity of the "back end" equipment requiredfor removing the captured flyash from the bed material. The use ofcyclones in series with magnetically stabilized cross flow contactorprovides redundancy in the system. The cyclones also provide aneffective margin of safety to prevent rapid catastrophic failure of gasturbine blades in the event of failure of the contactor. Similarly, themagnetically stabilized gas flow contactor can easily accommodate anadditional load resulting from cyclone failure, thereby, permittingshutdown and repair to the system without endangering the highlyexpensive gas turbines.

In typical pressurized high temperature fluidized combustion processes,the flue gas contains 2 to 5 ppm of alkali metal exiting the combustor.In order to reduce the susceptibility of the turbine blades to thedeleterious action of the alkali, at least about 99.6% of the alkali inthe vapor phase must be removed. To accomplish this objective, alkalimetal scavengers, in the form of metal oxides or mixed metal oxides, maybe used to remove the alkali metals. Examples of suitable metal oxidesare alumina, banxite, alundum, silica gel, diatomaceous earth and Kaolinclay. These scavenger materials may be suitably mixed with thecobalt-based magnetizable particles which are necessary to stabilize thepanel bed with magnetic field. The amount of scavenger used will besufficient to remove trace alkali metals to levels of less than 0.02 ppmby weight. However, this amount will preferably not exceed 25 wt.% ofthe total bed solids.

After the alkali metal scavenger has removed trace alkali metals, thesorbent may be separated from cobalt-based materials using a magneticseparation. Although it may be possible to regenerate the scavenger forre-use, it is preferable to use the scavenger on a "once-through" basis.Because of the low concentration of trace metals in the flue gas, even anon-regenerable system would require modest amounts of scavengermaterial.

In a typical example of the high pressure, high temperature combinedpower cycle process, flue gas from the high pressure fluid bed combustorat 1-2 lbs/sec of flue gas over a temperature of 1500°-1700° F. and apressure range of 6-16 atm is passed through cyclones to remove the bulkof flyash/dolomide particulates. The flue gas then is passed into amagnetic cross-flow panel bed consisting of an admixture offerromagnetic particles necessary to stabilize the bed and alkali metalscavenger particles such as bauxite or alumina. The stabilized movingpanel bed acts as a filter for capturing particulate by impaction,interception or diffusion on the bed material. Trace quantities ofsodium and potassium are removed by reaction or adsorption with thescavenger bed material. As the concentration of flyash increases on thebed, it is removed from the bottom of the bed and circulated by a gastransfer line to, first, a rough cut cyclone, which removes any flyashwhich has been detached from the bed material and, then, to anelutriator where the remaining flyash is removed from the bed material.Bed material is returned to the magnetically stabilized bed while thedust laden gas from the elutriator is combined with the transfer linegas and sent to a cyclone where the dust is separated from the gas. Theremaining gas is either cleaned further in a bag filter and sent to astack or recirculated to the combustor as makeup air.

As trace metals build up on the non-magnetic material, they are removedby "bleeding" a side-stream of particles and subsequently removing thescavenger bed material. This separation may be easily accomplished byusing a magnetic separation.

The key features of use of the magnetically stabilized cross-flowcontactor in the high pressure high temperature fluid bed combustionprocess are:

The gas velocity before bed material is entrained or "blown out" of thebed is significantly increased because of the orientation andstructuring of the bed material by the magnetic field.

Low pressure drop. The structuring and orientation of the bed results ina higher void fraction and hence lower pressure drop per unit thicknessof the bed when compared with a conventional moving granular panel bedoperating at the same conditions.

The collection efficiency significantly increased over conventionalpanel beds.

Alkali metals can be picked up by non-magnetic scavengers which areadmixed with the magnetic material.

Another use for the magnetically stabilized cross-flow contactor of theinvention involves using the same to control dust in grain elevators,flour mills and other operations with potentially explosive dust is asafety hazard. The presence of grain dust in grain elevators, flourmills and other agricultural and mining operations presents a potentialsafety problem. These problems may be handled by the use of themagnetically stabilized cross-flow contactor. For example, air purgestreams are used to remove dust from the silos, transfer points, loadingfacilities, etc. The air from these points passes through themagnetically stabilized cross-flow contactor in which the finely dividedsolids are removed from the air before it is discharged by an induceddraft fan to the atmosphere. In the magnetically stabilized cross-flowcontactor the gas flows in a cross-flow manner through a moving bed ofmagnetically stabilized solids. The solids are a very high densityferromagnetic material and can range in particle size from about 100 to2000 microns. Particle size is adjusted to control pressure drop andparticulate capture efficiency. The solids from the filter pass througha moving grate or a vibrating sieve which is continuously contacted withsuitable means to remove the dust. Solids pass from the grate or sieveand are transported back to the filter vessel. This system offers theadvantages of a very high gas velocity with a very low pressure drop.The panel bed thickness may range from about 4 to 24 inches andsuperficial gas velocities up to and excess of 20 ft/sec. can beachieved. A particular advantage of this system is that the grain dustis collected in a solid and is diluted so that it is non-explosive inthe filtering operation. As a further safety measure the solids arereadily washed with a suitable liquid which removes the dust, e.g.,water, from the magnetizable solids. The solids can be drained of theexcess liquid and returned to the filter zone.

While the invention has been described in connection with specificembodiments thereof, it will be understood that it is capable of furthermodification, and this application is intended to cover any variations,uses, or adaptations of the invention following, in general, theprinciples of the invention and including such departures from thepresent disclosure as come within known or customary practice in the artto which the invention pertains and as may be applied to the essentialfeatures hereinefore set forth, and as fall within the scope of theinvention.

What is claimed is:
 1. In a cross-flow magnetically stabilizedgas-solids contacting apparatus, comprising:(a) a chamber including aplurality of solid, discrete magnetizable fluidizable particles and aninlet means and an outlet means for continuously introducing andremoving solid, discrete magnetizable particles; (b) magnet or solenoidmeans for applying a magnetic field which is colinear with the externalforce field within said chamber; (c) a plurality of opening means insaid chamber arranged on substantially opposite sides of said chamberand being situated in such a manner as to permit gas to flow with avelocity component substantially perpendicular to the external forcefield and said magnetic field within said chamber; (d) at least twoplenum means, one of which is a gas inlet plenum communicating with saidopening means on one side of said chamber and the other, a gas outletplenum, communicating with the opening means on the opposie side of thechamber; (e) at least a pair of substantially upwardly extendinghorizontally spaced-apart perforate retaining walls, one of which is incommunication with said gas inlet plenum and the other of which is incommunication with said gas outlet manifold; (f) a plurality of louverseach adjacent said opening means in communication with said gas inletplenum, said support louvers being arranged to extend outwardly frombelow their adjacent openings and into said inlet plenum to support andexpose to the chamber a plurality of free surfaces of particulatematerial, said support members being arranged cooperatively to supportthe solid, discrete magnetizable, fluidizable particles and retain saidparticles within said space, the improvement which comprises: providinginlet louvers wherein a first portion of which extends upward andoutward from the openings toward the incoming gaseous fluid and into theinlet plenum and the balance, the second portion, extends outward anddownward toward the incoming gaseous fluid and into the inlet plenum toform a " " configuration.
 2. The apparatus of claim 1, wherein the firstportion of said louver extends outwardly and upwardly at an anglegreater than about 45° above the horizontal plane and the second portionof the louver further outward and downward at an angle greater than 45°to the horizontal plane.
 3. The apparatus of claim 1 wherein saidperforate retaining walls are a plurality of panels joined to oneanother.
 4. The apparatus of claim 1 wherein said chamber isrectangular.
 5. The apparatus of claim 1 which additionally includesmeans for regenerating said magnetizable, fluidizable particles, saidregenerating means being in communication with said outlet means andinlet means of said chamber.
 6. The apparatus of claim 1 wherein saidsolid discrete magnetizable, fluidizable particles in said chamber havea mean diameter particle size ranging from about 10 microns to about1000 microns.
 7. In a process for contacting a gaseous fluid with aplurality of solid, discrete magnetizable particles comprising:(a)continuously introducing and removing a bed of solid, discretemagnetizable fluidizable particles in a porous chamber in a descendingmanner or direction (b) structuring and controlling the porosity in saidbed by applying a magnetic field to said bed in a manner such that themagnetic field is substantially colinear with the external force fieldwithin said chamber; and (c) passing a gaseous fluid through themagnetized particles with a velocity component substantiallyperpendicular to the external force field and the applied magnetic fieldwithin said chamber, said magnetized particles are retained within saidchamber by the action of said magnetic field and a plurality of louverswhich are adjacent to the openings in the chamber, said louvers arearranged to extend outwardly from below their adjacent openings andtoward the incoming gaseous fluid to support and expose to the chamber aplurality of free surfaces of said magnetized particles, the improvementwhich comprises: providing inlet louvers wherein a first portion ofwhich extends upward and outward from the openings toward the incominggaseous fluid and the balance, the second portion, extends outward anddownward toward the incoming gaseous fluid to form a " " configuration.8. The process of claim 7 wherein the gaseous fluid contains entrainedparticulates and the contacting of the gaseous fluid with the magnetizedsolids removes a portion of the particulates from the gaseous fluid. 9.The process of claim 8 wherein the gaseous fluid additionally includessulfur oxides and the chamber includes a flue gas desulfurization mediumcomprising a pluraity of solid, discrete magnetizable particles whichinclude an acceptor composition capable of accepting sulfur oxides. 10.The process of claim 7 wherein the bed particles are continuouslywithdrawn and recharged into said chamber in a periodic manner.